Alot of artists use feedback in songs. Bands like Nirvana etc used it pretty regularly ie the end of Anueryism (I dont think thats spelled right). For a feedback solo try Drown by the Smashing Pumpkins thats got a big feedback solo at the end of it.
Basically feedback is 'white noise' which is picked up by your guitar played through the amp which in turn is picked up by the guitar even more and then played through the amp. This happens very quickly and you get a distinctive howling screech kinda noise.

Hope that helps

Neal