There are 5 computers in this house - 2 laptops, a Mini, a fire-breathing Mac Pro and an eeePC Hackintosh. My four all have Dropbox. as the King Shit of /r/favors, posting my referral link at the top of every Dropbox thread has given me 20GB free. My wife's has Dropbox. She's got like 10GB because she told all her friends. Both laptops write to the Mini's time machine. The Mini also holds select photos and all the MP3s and MKVs. The Mac Pro (and its 5 drives) back up to a 4TB Time Machine. The Hackintosh, other than dropbox, is without backup. I should maybe do something about that 'cuz it was a stone-cold bitch to configure. Back when I lived in two places I used to carry a drive with me on the plane and then conform both locals using Deltawalker. Now I pretty much lack an offsite backup but a lot of that has to do with the lack of satisfactory large file storage space. For collaboration I've used wetransfer.com for a couple years now. Works great.
"Data is only data if it's in two or more places. One, it's just cache."