Many iPad customers spent the weekend playing with their new devices, and several reported iffy Wi-Fi performance.
One thread on Apple's Discussion Boards describes a weak or inconsistent signal. "My signal keeps fluctuating from strong to weak, while my MacBook and iPhone show a consistent signal at the same location," writes user Andrew79. Another user writes, "Even when standing in front of the wlan router the signal fluctuates from strong to very weak."
I've experienced this myself. However, when my iPad's signal strength indicator fluctuated between one bar and four, it never lost a connection. So I'm inclined to believe that it's reporting the signal strength incorrectly, not actually dropping off and on.
Users in another thread report that their iPads connect, but can't get an address to get out to the net. " My iPad connects to my wifi without a problem," one user writes, "but the only site I can visit is my access point's web interface. I can't even get to my router's interface from the iPad. All my other devices (touch, laptops, Roku) can access the Internet without a problem."
I haven't had this particular issue. If you're having trouble, consult the iPad User Guide [PDF]. Specifically page 117. Otherwise, sound off in the comments and Discussion Boards.