I have the 105/dc; expensive but as good as it gets for nice blur in the background and clean sharp in-focus area.
I only have an f4s, and it has arrows to tell you which way to rotate the lens, and a green light to show acceptable focus.
A recent German magazine published tests of the AF accuracy of the current crop of DSLRs (OT - but they are likely to be at least as accurate as an F4, hopfully some progress has been made in AF since c. 1988), using many different lenses,focusing distances, subject types, etc. Different results according to brand: Canon was worst, with only something like 30% perfectly in focus, 20% acceptably in focus and 50% out of focus (going from memory here). Nikon did better with about 50% in focus.
This fits my own (fairly extensive) experience of AF usually not being as accurate as manual focus (at least with a decent viewfinder).
I'll get hold of of a copy the magazine sometime soon (I quickly read the test in a library): it really was interesting.
But if you find 100% perfect focus using the focus indicator light, then YMMV (and your quality standards too)...
OK Rol_Lei Nut, now the OP at least knows how you arrived at your one line comment but it would have been helpful if you'd said from the start that you believe that all AF systems are faulty in more than 50% of cases and this is based on your experience and an article on DSLRs.
If APUG is going to be useful in threads where the OP is seeking information then we all need to know why someone has said what he/she has said.
Thanks, I'll keep that in mind...
Sony's new NEX 5n and NEX 7 have a "focus peaking" function made for manual lenses that leaves little doubt about focus accuracy--a feature that should become common since Sony makes a large percentage of today's sensors.