Fix for PC Tools users
I finally found out why I couldn't connect to the iTunes Store when I upgraded to iTunes 10.5 ... turns out there was a bug in Spyware Doctor that was blocking the connection.
PC Tools has put out fixes for both Spyware Doctor and sister product PC Tools Internet Security, though.
For Spyware Doctor: http://www.pctools.com/kb/article/how-do-i-upgrade-to-the-latest-release-of-spyw are-doctor-with-antivirus-71.html
For PC Tools Internet Security: http://www.pctools.com/kb/article/protection-software-how-do-i-upgrade-to-the-la test-release-of-pc-tools-internet-security-85.html
iPod touch, iOS 4.3.2