A lot will depend on your expectations in terms of accuracy, as well as the equipment you're using and mostly, of course, your own skill and the style of shooting you do.
Myself, I use manual focus most of the time, often on moving subjects. My results are admittedly somewhat inconsistent, but there are plenty of other reasons for that :-)
I found that in the past I was occasionally let down by slow AF in low light... since my old camera couldn't be set to always take a photo as soon as the shutter button was fully pressed, I found that there were times when I'd have rather had a slightly OOF shot that caught the moment, but that this was denied to me by factors somewhat out of my control...
I met a Leica rangefinder user, who as you might imagine has quite impassioned views on the benefits of manual focus. I now echo many of these sentiments.
One thing to be aware of is that the stock focus screens installed in most SLRs are not apparently able to correctly represent depth of field at apertures larger than F/2.8. So, no matter how good your vision and skills, this will be a limiting factor in your results with wide open fast lenses. It is possible to replace the screens for ones with manual focussing aids such as split prisms. In the past, I brought a cheap one of these from an ebay vendor and found that it was badly calibrated or otherwise faulty for use with my camera at the time; many people regard http://www.focusingscreen.com and KatzEye as being worth the cost (I'm considering buying a new one at some point).
Now that I'm in the practise of manually focussing regularly, I may or may not be as fast as the machine would be in a given situation, but I feel a closer connection with the subject and process, and rarely am I frustrated by my equipment. I also don't alert my subjects with the sound of AF motors; so even though at times I may take several seconds composing and framing a shot, people often comment that they find my photography very unobtrusive. I realise that supersonic AF motors might mitigate the acoustic effect, but I'm not too interested as I now feel that MF is fairly integral to my technique.
I do frequently set focus to the right approximate range before shooting as well, particularly if I feel like my subject might be a bit touchy...