My 7d just took 21 minutes of uninterrupted footage. I thought there was supposed to be a 12 minute limit.

I think it depends on bitrate and resolution. 7D shots 12 minute long at 24p - 1080 lines. Shootins at 720p might double shooting time.

And don't forget, there's the 4GB limit per file, thanks to the FAT32 MC.

I have it set to 1080 24p with an extreme IV 8gb card in it.