2X adapters (any good?)

I have an Olympus evolt 500 with a 40-150 lens. Sometimes I just want to get a closer shot. Do 2x adapters work or do they degrade the picture. They aren't much on ebay (from $30-$70), but I don't want to waste money if they are junk. thanks

I've used a 1.4x with my Canon 70-200 f2.8L and noticed that the shots weren't quite as sharp as they were without but it was nothing that couldn't be fixed up in photoshop. I think it depends on the quality of the lens and the extender you're using.

My lens is a zukio 40-150 that olympus uses for their high end cameras so I think the lens is fine. the adapter is:
http://cgi.ebay.com/2X-Tele-Lens-FOR-Olympus-40-150mm-80-300mm-E-500-520_W0QQitemZ360171519423QQcmdZViewItemQQptZCamera _Lenses?hash=item53dbe53dbf&_trksid=p3286.c0.m14&_ trkparms=65%3A12%7C66%3A2%7C39%3A1%7C72%3A1234%7C2 93%3A1%7C294%3A50