Windows 7: Any commonalities in upgrade problems

I am just playing and was wondering if anyone has any thoughts as to what might be causing the biggest problems with the Win 7 in-place upgrades. Software only since my hardware is pretty much set.

I am going to install iTunes, and some anti-virus and whatever else you might think could be relevant. I was also wondering if the Digital River download error messages were involved.

Let me know soon. I will be going from Vista Home Premium to Windows 7 Home Premium.