A little bit ago, I went back to using multiple computers again. For a while I'd just done everything with a MacBook Pro, which was nice - only a single machine to maintain, always had everything in one spot. But alas, twas time for more performance, so I got a Mac Pro, which is now my primary work machine, with the laptop relegated to basically iCal and Things for the bulk of the day (as my 3rd monitor), and then any portable needs, or working on the couch or deck, etc.
Anyway, my main thing against multiple machines, after having spent many years with anywhere between 2 and 5 machines (mostly while working for Adobe), was the maintenance and synchronization of those machines. So, now that I'm back to 2, I am back to wanting/needing my data on whatever computer I'm using. These days this also really extends to my iPhone to some degree as well. It's my truly portable computer. So, with all the "cloud" computing/services these days, this is to some degree easier. I'm not that big a fan of Google having all my data, but I will use the services that are the best in class, or best for my needs, and no doubt some of that is Google, but there are many others.
I have not gotten all my data truly available on all the computers I want it on, or as well as I'd like yet, but I'm getting closer. Also, I agree with Al3x in that if the data is important, only having it on a free cloud service is not wise. I haven't fully followed that, but that is part of my plan. Here's some notes on what I've done so far...
This one is easy. I use Gmail for all my email accounts (about 15 if you count across various domains and so on). Right off, this is one case where this is the only place my data/email lives, so I'm only solving the accessible from anywhere issue. But, I'm also of the mind that I could pretty much lose all my email and be fine. If there are truly important things in it, that data tends to wind up getting put in somewhere else (EverNote, etc., see below) as appropriate. Gmail is so much better than any other Email. I even use it for some non-traditional things, like all our recipes are stored in a Gmail account. Makes it easy to trade recipes amongst friends and family, great for searching, and again, I can get to it from anywhere I can access the web.
Further, I use MailPlane as my actual mail client. It is a very rare day that I use a web browser to view Gmail. On the iPhone I just use the regular iPhone mail client, which has some drawbacks, but for my needs is ok.
Notes and Misc Data
This is the place that recently changed and has become an outstanding solution. I used to use 37signals Backpack, but now use EverNote. EverNote is really quite amazing. I hadn't noticed the Notebooks before, and that's been a great feature for me to do high level organization. Then, the searching is quite good (and of course Backpack essentially didn't even have searching). But, what really swung this over was their desktop client, web storage, and then iPhone client. This gives me great desktop performance, but then access from any web browser, as well as iPhone, AND I get the data stored locally and off-site (i.e. on the web). Furthermore, it sync's across computers. So, I feel like the data I have here is very safe (since it's in at least 3 places). Even better, this allowed me to stop paying for Backpack (my use of EverNote is nowhere close to their paid account). I don't mind paying for software at all, but I had felt that I wasn't getting the solution I wanted from Backpack, so didn't want to pay for that any longer.
GitHub and Git. Do I need to say more?
Two things here: .Mac and Delicious. I use Safari as my primary browser, and leverage it's Bookmark Bar for common stuff, so sync that across machines and iPhone with .Mac. Delicious gets all the other bookmarks.
Another recent change was to stop using NetNewsWire which I've used forever, and switch to Google Reader. Specifically what made this work well was creating a Fluid app with the Helvetireader styling. NNW had sync via NewsGator, but it really just didn't work well. It didn't seem to keep the list of feeds in sync, and then it's sync during feed download just didn't seem to cut it. So now, with the fluid app, and then just plain Reader (via browser) on the iPhone seems to solve this all nicely.
So far this is a mix of using DropBox and Google Docs. DropBox is awesome for keeping files in sync across machines, and then also available on the web. I've been ramping up my use of DropBox.
Things that Aren't sufficiently solved yet
Update: I'm now using .Mac to sync Address Book, seems to work great.
I'm using iCal and Address Book. Primarily this is due to the super easy sync with the iPhone. I can sync two computers with BusySync or some other things, but haven't seen a great solution yet, as well as haven't investigated that much. Even with .mac I think you still have to have a primary calendar and you're publishing to the other, etc.
I've used Google Calendar in the past, but didn't like it that much, and part of all this is ensuring sync is brain dead easy and solid. My wife and I sync calendars with BusySync, but that has been spotty. The various Google/iCal sync things I've tried have been iffy in the past. And, the real key is, how well will it sync Google cal to the iPhone calendar? An area I need to learn more about.
Address Book, not sure of my options here either. Sync's nicely with iPhone, and .Mac so far.
Music and Photos
I've yet to see an iTunes sync thing that works really well. We tried TuneRanger but it was not good when dealing with two existing libraries. Also, we have a lot of music, so keeping it backed up on S3 or similar actually starts to cost real money. Of course these days, the primary need for this is to sync to my iPhone. Most of the time at home I'm listening to Pandora or some similar thing. I use Pandora a lot on the iPhone, but I also listen to various podcasts, and then there are times when Pandora isn't feasible (crappy/no signal, or I'm needing to use another app on the phone while listening to music).
These same issues hold true for photos/Lightroom libraries. With Lightroom so far, for each calendar year, I have a Lightroom catalog, and then at the end of those years, I burn DVD's with the photos. Of course, the DVD's are just sitting in our house right now, not in a safe deposit box, etc. (we used to do that, but haven't since we moved to Oregon - lazy). But my bigger concern here is that I'd like my Lightroom library to stay in sync across my two machines, so I can use the burly Mac Pro when working at home, but then have my MBP when on the road.
I guess that's it for now. What solutions do you like? What are people doing for large data (GB's or TB's of music, photos, video, etc.)?