As described by lots of users in the Apple support forums, Wi-Fi connectivity slowed dramatically after the upgrade. There seems to be no rhyme or reason to the slowdown, as it is affecting new and older iPads, people using Apple or third-party Wi-Fi routers, and a number of other variables.
Apple doesn't appear to be acknowledging the problem, much to the extreme frustration of iPad users who are having the problem. On the other hand, it may not necessarily be a widespread problem. A quick survey of TUAW bloggers showed that none of them are seeing the issue, and none of my iPad-toting clients are having the problem (trust me, I'd hear from them).
We're curious to see what percentage of our readers have seen this problem with their iPads after the late November OS upgrade. Please take our (unscientific) poll and let us know.