My SO is still using a 13" early-2011 MBP, recently upgraded with an SSD and 16GB of RAM, and running the latest OSX release. With only it's original 4GB of ram it was constantly swapping on more recent releases of OSX, which was pretty painful, but it operates just fine now. A brand new 13" MBP would have longer battery life, weigh less, and have a High-DPI display, but wouldn't really be any faster in day-to-day use (and it wouldn't even support more RAM!). I was pretty surprised by how little computers had improved in the last six years.
That's my daily driver. It's amazing. I looked at About This Mac recently and was shocked that it's 6 years old! I could've sworn I had bought something newer. Time flies on a good machine.
I'm more of a PC guy, but I have to admit, I really liked it. Good screen, great keyboard and touchpad. Good battery life once I swapping in a new pack.
(Significant minus for those stupid non-standard screws, though.)
I could easily see using one as my daily use machine if I was in a more mac-centric environment without feeling like I was missing anything at all.
