mine was also broken about 2 weeks ago. it stopped clicking and would take a very hard press to work. i was way past warranty since i got it at launch. i also don't want to give it up since its unlocked and can fetch more cash than what apple might replace it with...also, out-of-warranty replacements are $200 i believe.
for me, i didn't need to replace the actual button although i did buy one for about $5 on ebay. i needed the ribbon cable underneath which you can see in the pictures (towards the end, with the little orange circle clicker thing). you can also buy the ribbon on ebay, also around $5 i think.
its a lot of work to replace the stupid ribbon though. the screws are tiny and of a bunch of different sizes. but its do-able...took about 1 hr for the first go around.
edit: if you don't feel like DIY, craigslist has people that offered repair services. i called some and they wanted about $50 for the fix
I cannot get one under warranty. I am 95 days past my warranty. The button does not actually click at all and does not work at all.. It is almost like it is stuck pushed down.