iTunes' podcast section was horribly laggy for me, also the iPhone podcast sync management tab. My hard drive would thrash, and iTunes would be unresponsive for 5-20 minutes (tested across several reboots and cold/hot iTunes restarts) while I could use the rest of my computer just fine.
I found two distinct fixes:
1. Temporarily disable ALL connections to the internet, whether they can connect or not. This cuts down the lag significantly to less horrible 1-2 minutes in iTunes, 30-60 seconds iPhone podcast management tab.
OR
2. Go to Edit > Preferences > Store and uncheck "Automatically download album artwork". This got rid of almost all lag, making iTunes 11.1 (and iPhone sync management) about as fast as 11.0.5 was, maybe even a bit faster.
It seems that something has gone horribly wrong with iTunes' procedures for checking album artwork for podcasts -- maybe it's checking artwork for each individual file until it finds something, or maybe it generates a new artwork cache EVERY time you load the Podcasts category. In any case, I don't really make much use of the automatic artwork downloads, and unless you're importing a bunch of CDs, you probably aren't either. Even so, you can still right click on media to search for missing artwork if you need it.
EDIT: Huh, solution #2 seems to have inadvertently fixed another problem I was having with iTunes 11.1: not being able to delete podcasts in "List" view. Now I can actually delete podcasts again! If only there was a way to not have all the old episodes still showing....