I'm trusting the google cloud for all of my email and calendars and contacts. I use Flickr but just to share - I keep the originals of all of that information on my computer. And all word processing and spreadsheet and financial stuff I keep on my home computer, with only a cloud based data backup for some of the key stuff that I want backed up locally AND in the cloud.
I like Dropbox for its automatic sync between devices and computers (I have it going between the iMac, the netbook, the iphone and the iPad) but another similar (and more generous with space) place is Sugarsync. Many of these places also give additional space if you refer people, but I won't put my link here. You can only "earn" a max of 10G at Sugarsync, I think I'm almost up to 9.
Other places to check out: Evernote: multi device use, can generate new documents with the app. ZumoDrive 2G free. I've never used it seriously, but its available for nearly everything.
And for an alternative to Google apps Zoho Office: Gets you cloud computing, collaboration and email address as well. Windows Live: Its not just about hotmail and MSN anymore. You can create and edit Office docs online now. you also get 25G space.
There's so much out there, you just can't possibly keep up with it all, or even use it all.