I’ve been testing out Dropbox as a way to sync my 1Password files between computers (which works really well) and, more experimentally, to share a single iTunes Library (which… doesn’t work so well).
A few days after installing it, I started getting “Your Startup Disk Is Almost Full” messages. Having had a similar experience with a client who was backing up to Apple’s .MAC service, I quickly zeroed in on Dropbox as the culprit. A quick bit of Google-Fu found other people having the same issue — and it also found a solution.