n99127: Razer mice vary greatly in terms of quality/ergonomics. People have already mentioned the Lachesis as being a poorly designed mouse, and I tend to agree.
I personally use the Razer Naga, which I feel is nice, though I don't use the buttons on the side except for a handful of games and tasks. It has a nice fit and moves very smoothly on my mousepad (which, incidentally is a Razer Megasoma).
I also have a Razer Mamba, which is kinda nifty because it is both a wireless and wired mouse, but the wireless receiver is REALLY bulky (it has roughly half the footprint of the Mamba mouse itself). It also has the tendency to tilt on its side a tiny bit on some surfaces.
I had a copperhead that was a good mouse wear and tear over the years lasted a good while and had good features I would recommend to people who like to have all the side buttons, It lasted about a couple of years the buttons wore eventually and it wouldnt register but over 300 clan matchs in cod4 was the main attribution to that.
I had a razer lachesis and it pissed me off so much I literally threw it against the ground in a rage as the side buttons had a habit of getting stuck on the profile switchs inside the mouse resulting it being unusable as it would constantly switch profiles. Lasted about 8 months before I threw it - had problems about 4 months in had to unwedge one of the buttons with a knife
I now own a razer abyssus and its prob my fav of the lot, ambi and basic, I just like it fast and dont like/care having 20 buttons either side my hand. doesnt need any software and you can sinply adjust the dpi and polling with switchs at the bottom
It sounds extreme but be sure to measure your hand and look at the prefered grip style before buying to ensure you can hold it at your prefered position
I do throughly recommend the razer exactmat/exactrest as well esp if you game/work a lot it has saved me from carpel tunnel singlehanded. I use a tarantula keyboard as well and agree definately the best brand ive seen the cost is a reflection of quality in this instance