There's a program for Thinkpad laptops called TPFancontrol, that allows you to set the fan control how you want it. Mine idles at 40-50C, with the fan completely off. The first 1 or 2 levels of fan spinning are quite inaudible. Some people have an issue with the fan 'pulsing' (spinning fast very briefly) but I've only rarely noticed the issue - mostly in the late hours of the night. For me it seems to occur on the border between fan off and fan on, and this point can be adjusted to fit your needs.
I'd definitely recommend reading up on the Lenovo and Notebookreview forums to see what issues people are having. Lenovo seem to be actively developing BIOS fixes. I also considered other laptops ie. Dell E6420 and HP 8460W, but this one matched my needs best.
My machine specs:
2720qm
8gb ram
FHD 1920x1080 matte screen
Nvidia Quadro 1000M
Intel 310SSD 80GB (Soon to have Crucial M4 256GB)
9 cell battery
3 year warranty
BIOS 1.26
TPFancontrol base install:
http://www.staff.uni-marburg.de/~schmitzr/donate.html
TPFancontrol for W520:
http://forum.thinkpads.com/viewtopic.ph … mp;t=96275