API v2 - set metadata/mtime

We'll certainly consider this, but I'm curious if you've considered keeping track of revs for syncing. This has a few advantages over using timestamps:

1. It allows you to sync correctly with more than one computer (without having to have strict clock synchronization requirements).
2. It allows you to sync correctly even if the time on the local computer changes (e.g. due to correcting clock drift or even things like leap seconds).
3. It allows you to know when you can safely overwrite a file in Dropbox. (With just a timestamp, you can't tell whether or not a file was modified in the cloud since the last time you uploaded, so you don't know if an overwrite might destroy work from another computer. A conditional upload with a parent rev also avoids clobbering a file in a race condition where the file is modified remotely during an upload.)

FYI, I'm pretty sure the Dropbox desktop client never uses the client modified time at all (though it does set it so it matches the local filesystem).

I suppose the downside of using the rev is that you have to keep track locally of what the rev of each file was the last time you uploaded/downloaded, but this is a small bit of information to track per file and helps avoid correctness issues with your syncing (that could lead to data loss).