Summary: I installed this printer a year ago at a non-profit I work for. It has a couple of gotchas, which caused us massive grief for a few months. If you print via the Internet Printing Protocol (IPP), the printer will crash periodically on seemingly random jobs. When it crashes, it doesn't automatically reboot. Reconfiguring your print server or desktops to use the LPD (or other protocols) will fix the problem.
Summary: Comments about Lexmark T640tn: This printer didn't float my point. I'm not sure if it is my computer or the printer, but the PPM was terribly slow. I can't work with this printer. I would NOT recommend any purchase this printer. On top of it being pricey, it is slow and noisy.