PAE or not to PAE

Has anyone here tried PAE to utilize more than the three and a half Gigs memory limit? I have also read that XP with no later than SP1 can utilize more than that anyway, so I could use a computer not connected to the net if necessary (not having to worry about viruses), to be able to utilize 4 Gs or more memory. I think I read that Microsoft found some programs weren't able to handle the upper addresses or something, hence putting in the limit in later SPs.

I know I could upgrade the OS, or get a copy of XP64. I would just like to know if the upper information is correct and the results you had if anyone tried it.

Thanks.
Dean