From my experience as an Electrical Engineer and years of experience supporting my company's users' cell phone population (for what's it worth), I'm thinking this all is hard to troubleshoot. Any WiFi technology, especially when you do *NOT* restrict it to (say) Apple Airport Extreme WiFi Access Points, is going to end up with a mess. And here we are, with a number of iPad users having issues.
My WiFi iPad has had no problems with an AEBS and also at work with HP Enterprise Access Points (but, note they are only G!), but I don't doubt all the issues everyone's having. It's a mix of what encryption, what band (N, G,.. ), multi-band, etc., and the hardware in place.
I started off 18 months ago with a Verizon FiOS Actiontec Router. My iPod touch wouldn't connect reliably. I suffered until I got an iPhone last summer (3GS). It also sucked connecting to WiFi. At that point, I got really pissed. After researching various Windows WiFi routers and access points, which all had middling reviews, or sucked, I said F this, and got an Airport Extreme. Instantly my Macbook, iPod touch, iPhone, and (now) my iPad all work perfectly Note that my Dell (sorry) also works perfectly.
So, perhaps the moral of the story is: Apple implements WiFi properly?