After all the controversy, criticisms and pixel peeping on the web, I was expecting to have to return this lens at least a few times before getting a 'good' copy or at worst - a refund (out of curiosity my copy was made Dec-08...).
What can I say, I was pleasantly surprised. Its a fantastic lens and if like me, you love a fast discreet 50mm for street/ low light photography then it's defintely worth the investment. The pictures have a certain vibrancy over other lenses and the build quality is absolutely quality.
The lens is not especially sharp from f/1.2 - 1.6 and has noticeable purple fringing at these f numbers (but definitely useable). It becomes sharp by f/2 and tack sharp by f/2.8. Comparing it to my 24-105mm, it's MUCH sharper than the 24-105mm up to about f/4.5 - 5. By f/5.6 onwards they are much of a muchness, although the zoom is a tad sharper in the corners.
I tried to recreate the focus shift issue, but couldn't find any problems. I've maybe had 1 or 2 slightly missed shots at the minimium focus distance of 45mm, but then I've had that on rare occasions with my 24-105mm too. It's always asking for trouble when you shoot at the min distance for any lens. On the whole I would say the lens easily focuses as accurately as my 24-105mm, and perhaps a split second slower due to the front glass element moving through the barrel (which incidently means you need to get a filter to make it dust and moisture resistant - doh!)
Overall a marvellous investment that will last, unlike the (also excellent) 50mm f/1.4. I think the biggest complement I have, is that this lens allows me to shoot the way I want, without having to change my style to accommodate any functionality/design issues - and for that reason, its almost always attached to my 5D2