Same issue with Belkin N+ and iPad and possible fix
I've had the same ongoing issue with my iPad dropping wifi while connected to my Belkin N+. I have the opportunity to test scenario's because I have an N+ at my home and one I installed at my parents home. I was experiencing the same issue at both places. The symptoms are that the connection times out unless I am actively browsing or doing something else to use the network which keeps the connection alive. For example, if I leave Pandora running, my connection stays alive indefinitely. The connection drops after about 3-5 minutes of inactivity. The only way I've found to reactivate the connection is by turning wifi off in Settings and then turn it immediately back on.
The issue seems directly related to the wifi security method. I had both routers set us to use WPA-2 with a passphrase (by the way, my 24" iMac has the same exact issue with dropping WPA-2 wifi connections). I changed the wifi back to WEP (128 bit) and haven't had an issue with dropping wifi since.
I've played with all the Belkin settings related to multi media, etc. The bottom line seems to be an incompatibility between the Apple and Belkin implementation of WPA-2. Who's right? Well, I can tell you that I have 4 PC's between the two locations running Windows 7 and XP Pro that never had issues dropping wifi with the Belkin N+ set to WPA-2.