We fake our designer using Git. He has access to each repo's view and static asset files through a Samba share. Every afternoon we ssh in and commit his changes. When he says stuff is in good shape for the next release we merge his branch to staging. And whenever it's a good time, we merge stag down onto his branch so he has all the newest stuff.

So far it's worked great.

SparkleShare (http://sparkleshare.org/) uses Github to replicate Dropbox functionality; could you use the SparkleShare client on your designer's workstation so that when assets are created/updated/saved, they are automatically committed to your repo?

Thanks, I'll look into that.

Awesome! Let me know how it works out!