I have the same exact issue. I have cleared my settings, (although I don't think that is going to do anything), and I've reinstalled the firmware. So far I haven't had any freezes, but I haven't been able to shoot much - just keeping it by my desk at work and testing it out. (Shoot, let it go to sleep, shoot, let it go to sleep - no issues yet.)
Note: on the second firmware update I did two things differently than the first time:
1.) I took off my canon battery grip and only used a single battery. (My theory being - the issue could be related to the grip.)
2.) I powered down and took the battery out after hitting "OK" that the firmware was installed. Last time I updated the date/time/location before turning off and removing battery for 10s. (Instructions say 2s, but hey - I'm trying to fix my baby here!)
I'll keep you updated if I have any freezing issues after the second installation.
Thanks for the suggestion. I will try to reinstall without the grip and see what happens. It is weird though because it can so to 'sleep' and wake up most times then right in the middle of using the camera it will freeze. So sometimes after sitting and sometimes while using.
Will have to try tonight--