Ok...so today I get my tire replaced as I had a big 'ol nail stuck in the rear tire. This being the third nail in the last three months. I took it to this shop I go to as a last resort not 'cause their service sucks but bexause they are kinda pricey inservice but they always seem to have what I need wheneveryone else doesn't. Anyway in changing the tire the mech. Told me I need a new chain and sprocket soon. (He bike only has about 4500 miles on it. ,ow considering wear and tear is this possible or am I doing something wrong in my riding...?

Wow - I can't imagine wearing out an O-ring chain in 4500 miles.  Talk about pricey service!  

Still, it wouldn't hurt to do some checking on your own.  These items scanned from the Clymer and Haynes manuals should help:

http://www.bbburma.net/Scans/Haynes_DriveChainWearCheck.jpg

http://www.bbburma.net/Scans/Haynes_Sprocket_Wear.jpg

http://www.bbburma.net/Scans/Clymer_Sprocket_Wear.jpg[/list:u]
PS - I replaced the stock chain on my '99 (an X-ring chain actually, with 520VM stamped on the side plates) at about 18,000 miles.  I replaced my front sprocket at the same time, although I didn't really need to.  At 34,000 miles I'm still on my 2nd chain and original rear sprocket.