Hi,
We're running a 1.0 installation, no caching, and IMAP proxy as a web client to Gmail. Everything seems to work fine with only one real issue: when "Refreshing" (either automatically or through the Refresh button), it takes around 25 secs to complete the operation. The issue would be lessened if other operations could be performed at the same time but pretty much the user is locked out until the refresh is done.
The caching options didn't seem to do much with respect to this operation so that's why it's off. I couldn't find anything in the Performance wiki that seems to make any difference on refresh times.
While it is checking all folders for new messages (and I can appreciate how expensive that is), when I login, Roundcube is ready-to-go in < 3 seconds. I've been using that as a benchmark as w/o caching, Roundcube would have to load up everything on startup by access the IMAP server. If anything I'd have thought a Refresh operation would take less time.