I've had the Pentax M 50mm 1.7 for about a month now and have had a few chances to use and get the feel of it. Shooting in Kyoto was a lot of fun being a much more dynamic city than where I currently live so obviously shooting opportunities were readily available. Before I went to Kyoto I happened to be looking through some of the Pentaxforums threads about using M lenses on the K10D and this is what I basically learnt;

Switch to M mode

Focus the shot

press the Green button (light meter)

Shoot

So far, this seems to work pretty well and I have no complaints about this lens. It has beautiful, creamy bokeh, it's sharp and easy to focus with.