Something I've been noticing in a few Lync (and Exchange) deployments where Forefront TMG is involved is a significant delay in loading websites through the reverse proxy. I generally use Chrome as my primary browser and noticed sites would be extremely slow to load or appear entirely unresponsive when published through TMG. This was happening to both Lync Web App and Outlook Web App scenarios so I figured the issue just had to be with TMG. After some digging it turns out the problem is Chrome because when browsing to these sites in either Internet Explorer or Firefox the pages load just fine.
The issue here is a new feature in Chrome called SSL False Start which is supposed to speed up your SSL connections. Unfortunately, the end result against sites published by TMG is they don't ever load unless the user manually refreshes the page a 2nd time. Keep in mind this applies to any SSL website published by TMG and accessed by a user with Chrome, not just Lync Web App or Outlook Web App.
There is also an issue open on Google Code about this problem, http://code.google.com/p/chromium/issues/detail?id=67617, but there is no server-side fix. At this time the only solution is to modify the Google Chrome shortcut to disable the SSL False Start feature. Just modify your shortcut to be "chrome.exe -disable-ssl-false-start" and all is well.