I was looking for such a feature when I installed my first HTPC, three weeks ago. I actually couldn't believe that neither 7MC nor XBMC support refresh rate changing based on the source frame rate.
I don't understand why auto-refresh-rate-changing isn't implemented on the most popular Media Centers for best possible playblack experience.
In the meantime I figured MediaPortal supports auto-switching refresh rate. But since I spend two weeks to setup 7MC/MediaBrowser properly I don't want to swithc to MediaPortal. So I have set my HTPC to 24Hz and only watch 24p sources for now. Btw, there is also a 7MC plugin to change refresh rates, search hack7mc.com
These frame rates should be supported
for PAL (25fps): 50, 75, 100, 120, ... Hz;
for NTSC (29.9fps): 60, 90, 120, ... Hz;
for film (24fps): 48, 72, 96, ... Hz.
In order to prevent tearing and get smooth video playback this is a MUST HAVE feature for every decent Media Center.