I've got a 60d and might upgrade to another body sooner or later. Having used the af system of the 60d - which is the same of the 40d/50d afaik - for over a year I am wondering what's the much praised af systems of the 7d or 5d(3)/1d are actually good for. Imho the 60d hasn't got a working af, but rather a "focus helper", but it works ok for static objects with a little recomposing. For moving objects, it does track them, but choose "servo af" is all you can customize.
Obviously, more expensive af systems have better low light capability, higher precision and higher speed. But apart from that...
* What features of the "pro" af systems really do make the difference for you? Can I tell the af to constantly backfocus so I have the eyes of a portrait in focus instead of the nose? Do these af systems remember which (part of a) moving object is tracked even if obscured from time to time?
Obviously, more expensive af systems have better low light capability, higher precision and higher speed. But apart from that...
* What features of the "pro" af systems really do make the difference for you? Can I tell the af to constantly backfocus so I have the eyes of a portrait in focus instead of the nose? Do these af systems remember which (part of a) moving object is tracked even if obscured from time to time?