I have had a ThinkPad Edge 15 for just over a year now and when SWiMBOs laptop expired I bought her the E520. We are delighted with both, the offset touchpad takes a little getting used to until one realises that it is centred on the keyboard and the addition of the numeric keypad means it has to move across. Incidentally I now swap machines when I have a lot of numeric work as the numeric keypad is a welcome addition on the E520.
The touch pad is fine but can be over sensitive for gestures which means in cramped areas you can accidentally zoom or scroll when you don't want to. I have turned of the gestures feature for both of ours and all is now fine. I am a lifelong TrackPoint (Nipple) fan so only leave the touchpad alive for those who borrow my machine.
One of the other factors I always weigh into the financial decision is the extended warranty. With laptop repairs so costly I always add a warranty extension to 3 years. On more than one occasion it has paid for itself enough times over to cover the times I did not need it.