I've had my USP Tac. .45 for about 2 years now, albeit I've probably not shot and cleaned it as much as many on this board. Today I broke it down to clean it and when I went to put the slide back on, it snagged a little when it hit the rear rails( the little part with metal embedded in plastic on either side). It seemed to shave a little bit off the plastic. Is this something to worry about or is this normal?
 Thankls in advance...

Normal.  It is completely normal for the plastic around the tabs to break off during use.  It freaks everyone out at first but I assure you it is completely normal.  So long as the metal tabs are still there everything is AOK.  I have pistols with no plastic left at all around the tabs and they are still as tight as when they were covered with plastic.  The plastic oozes up around the tabs during the molding process and since it just flakes away without harm, there is no reason to make an already expensive gun even more expensive by paying someone to cut away the flashing.

Quoted: Normal.

No, it's NOT! You've FUBARed your USP!!!!!    

However, since I'm such a nice fella, I'll give ya $50 for the worthless thing so you can go shopping for a new one..................