I've been having the exact same experience. After upgrading to Mountain Lion, I'd say it's gotten a little worse.
Problems:
1) If TV has been dormant for a few hours/days, then I have a 50/50 chance of it connecting properly to a remote Win7 PC. If it fails, then I usually have to force quit TV using OSX's Activity Monitor in order to retry the connection successfully. This reliability issue seems to have gotten a little worse since upgrading to Mountain Lion.
2) When I launch TV again, I get the "TeamViewer wants to make changes..." prompt for a password. Ugh. So sick of passwords.
3) Lastly, I have to leave the TV window + TV "Computers & Contacts" window open in order for my Mac to be seen and available to control remotely on my partner PCs. Maybe I have something misconfigured, but it's not obvious to me.
Despite these problems, I'm still a huge fan and love TeamViewer on Windows and my iOS devices.