Windows Phone 7 drops your WIFI connection when the handset is suspended, which is in fact a waste of battery life, as push services then use the 3G connection, which is not only more expensive, but a much bigger battery drain.
To solve this issue Windows Phone Hacker created a home brew app, Keep Alive, which uses a variety of background services to maintain a connection to his server, which stops Windows Phone from dropping the WIFI connection.
Jaxbot has now for the first time submitted the app to Marketplace, and it appears to have sailed though certification as a CPR app (which is probably an issue all by itself).
In any case the app is now available to all, not just those with a developer unlocked device.
The app is free and can be found in Marketplace here.
Read more about the app and service at WindowsPhoneHacker here.