I bought this laptop a few months ago, mainly because of its full-sized keyboard and its reputation for quality. Here's some notes if you're considering one.
First, a few details. I got a dual-drive RAID-ed model, with the second drive in the DVD drive bay. It's got a quad-core i7, and takes up to 32GB of RAM. Crazy. I ordered it with 4GB of RAM, and bumped it up to 16GB of RAM after purchase. 32GB is a crazy amount of memory, and those 8GB sticks are quite expensive right now. I did splurge for a 128GB SSD drive that fits into a peripheral mSata slot, once shipped to Canada it was about $200. I renstalled Windows 7 on it and it smokes.
The biggest problem I have with Windows 7 on this machine is that it often fails to come out of sleep mode. I'll be moving to a Debian Linux very soon, though I'm not confident this problem will disappear.
The biggest plus is that with the SSD, the battery lasts eight hours. The screen is great. The keyboard is awesome, though I can't understand why the lower left corner Fn and Ctrl keys are reversed (there is even a BIOS option to revert these to normal). Some sort of IBM legacy strangeness happening here.
The weirdest feature is how much the battery sticks out of the back of the machine, a full inch. It hasn't really been a problem for me, but it is something to pay attention to when buying a sleeve or bag.
The fan hardly ever comes on, and my hard drives hardly ever spin, because I'm working off the SSD the majority of the time. I've read complaints about fan noise and heat, but I have not experienced any of this. Quite the opposite, it's cool and quiet. (Disclosure: last laptop a Dell 6400 15.4", for about 7 years, and my only laptop. Loved it, replaced the mousepad and three keyboards, but it still works fine. Though it never bothered me the Dell got hot and the fan blew often.)
In time, I imagine I'll replace the two RAID-ed spinning drives with SSDs, but I've put enough money into it for now. I feel like the capacity of this machine has me ready for another decade of laptop computing, and I am quite happy with my purchase.
I have read some negative reviews of Lenovo products, and the W520 in particular, before I purchased it, so just wanted to put this out there. I'm not a fanboy or an employee, just a programmer who was looking for a kick-ass machine. In my opinion, the W520 is it.