I just got a fresh install from Mint 7 RC1, and got everything updated, through the Synaptics, since I also perform some tweaking and cleaning useless packages.
Those updates set me up to the MintSystem 7.4.6 and MintUpdate 3.7.6
Now, I can't seen to use the MintUpdate tool. The process is similar to other bugs described here: It starts looking for updates then it freezes (turning gray) and stays there.
I managed to get the following error message on the terminal everytime it crashes:
-- Exception occured in the refresh thread: unsupported format character 'a' (0x61) at index 10
Hope it helps the developers!
Ahh and also, having loads of fun with the new distro!