For everything that doesn't need to be on your own machine, find web equivalents that let you download regular backups: Bookmarks on Delicious, photos on Picasa, blog on WordPress, books on LibraryThing, development projects on GitHub, feeds on Google Reader, and CAD drawings on Thingiverse.
The ultimate tool at home has gone from CVS via Subversion to Git. The learning curve is steep, but it's liberating at the end to know that all the data, in all its versions, are on all my machines and will not get lost bar some really serious happenings. This is for the personal documents, application settings (useful to have the same everywhere) and of course development projects. If you want to forget old stuff, a git rebase --interactive is just the thing. To handle multiple projects which mostly just need to be pulled from a different machine, I've developed fgit, a simple script to run a git command on all repositories below the specified directory (or the current one, by default). Thus, to update everything when moving to a new machine, it's simply fgit pull -- ~.