Well I have first hand experience of it going bang above about 2G. It seemed to be a bit less though. It could have been a 2 000 000 000 bytes maybe instead of 2 000 MB or 2GB. I'm pretty certain that it will definitely break though.

And their "fix" is simply a dodgy program that uncleanly cuts off a selected number of megabytes off the end. You then go and run the scanpst to fix the .pst that you just corrupted. And what you cut off you lose of course.

The program didn't even work for me so I wrote myself a new one to do the job for me (properly)

See
http://support.microsoft.com/default.aspx?scid=kb;en-us;266709
and
http://support.microsoft.com/default.aspx?scid=kb;en-us;305108