My iPod touch 2nd gen and iPad 1st gen (WiFi+3G) have dropped their connection on a regular (and occasionally very frequent) basis ever since I've had them until just a few weeks ago when we replaced the Netgear DG834G wireless part of our home setup with an Airport Extreme.
Now the iPod touch, my iPad and my partner's MacBook Air are connected 24/7 and we love it ... but my brand new iMac can drop the WiFi twice in 20 minutes. Sigh! I've had to go back onto Ethernet but that's not an option with the iPad.
So, replacing your wireless router may help other than than I can't offer other help, sorry.
Stephen
Anxiety does not empty tomorrow of its sorrows, but only empties today of its strength. - Unknown