If you share a lot of files with colleagues via Dropbox, here's a potentially useful enhancement: you can now attach comments to files.
If you mention another user using an @ symbol in the comment, they'll be automatically notified of any changes. Sounds like a potentially handy alternative to digging through an email chain. You can also disable comments for specific files if you wish, and unsubscribe from notifications if you don't want to follow any further comments.
Dropbox blog [Dropbox Blog]