I have Keepass and Dropbox on my flash drive just in case I ever need to access something when using someone else's computer, without having to worry about keeping my password database up to date. Much easier than downloading Keepass on a computer that isn't mine--rude at best, not possible due to permissions at worst--and then downloading the database from the web access and cleaning up when I'm done.

It's helped me once or twice; not often, but the relatively small files on a multi-gig drive is worth it.

If you're dropboxing large files, using a lookaside cache means that you can greatly reduce latencies and often improve throughput (assuming you're not on 1 or 10 gigabit directly to the dropbox servers). But I doubt the dropbox servers themselves support this kind of functionality.

More likely is that you can move your files to various disconnected computers more easily and automatically without dealing with manually pushing them around from dropbox folders to portable drives.

I want my Dropbox stuff available to me in the office, but it's not my computer, so I'd rather not install the regular Dropbox. And going out to the web client is a lot less convenient than just having a file there locally. I've been wanting something like this for awhile.

It's not so much a thumbdrive, but disk space that I own in the office.