Just my tuppence:
I had a Razer some years ago, it was a Microsoft Habu in blue. Was about 5 years ago now.
I still have it and it still works. sometimes.
Was a fantastic mouse when I got it for 50 quid, and for the first few months it lived up to everything on the box.
But, after a while and what I would consider normal useage (for a gaming mouse) it started to get a bit buggy. The mouse would disconnect during use, usually at a critical point (just before that headshot on CSS) and I'd get that horrible "ding-dong" of windows telling me I had unplugged something.
Apparently I'm not the only one and apparently they haven't really fixed that issue, I've heard other bad things about build quality in general.
IMHO, if you want a good mouse that will last, try a Mionix Saiph. Got one for free with a PCGamer sub, it's served me well for over a year under heavy use. I think it's 3200DPI, a few extra buttons, on the fly sensetivity adjustment and a weight system. Cable is much more hefty and I like the feel of it.
Review here: http://xsreviews.co.uk/2011/02/mionix-saiph-3200/
Obviously if you're looking for > 3200, this wouldnt quite cut it but I've never had a problem with it, and I do alot of gaming - personally I'm not convinced that DPI matters that much when you're above a certain level.
The only other mouse I've used that I would recommend is a Sweex PS/2 optical mouse. Cost me 1.95 from Ebay, used it for 5 years, gave it to a friend who still has it. I must have fragged a thousand noobs with that thing, best buy ever.
EDIT: got the name of my mouse wrong. thought it was a copperhead for some odd reason... doh!