Members who have faced this problem find that going into Settings, WiFi and then telling the iPad to forget all the WiFi connections, then establishing them again, sometimes fixes the problem.
If you have other Apple products or are interested in other Apple kit then why not join our sister forum too at http://www.appleforums.net/
Finally, if you still haven't had enough, how about a video explaining about our other forums (note:you may want to play this at half speed but hey, why shouldn't Phil be excited about our forums!)