Is it better to try to get through PhD studies as quick as possible (as in UK) and start applying for post-docs, or is it better to spend a lot of time (as in US), and then be out on the "market" later but hopefully more prepared? Would like to hear what all of you think, although my particular field is molecular biology.

As a postdoc you earn money while you gain experience; as a PhD student the pay is lousy (and towards the end you're not even paid)while you gain experience.

Even in the US there is a lot of pressure to get the PhD students "out" and working. Hanging around in a degree program looks badly now on a CV as it looks as if you couldn't get it together to get something done.

I would be interested to know what you consider as a lot of time in a PhD program.

Well, I'd say more than five is rather a lot. Do the lab rotations and coursework in some programs really help or is it better to start with "real" research asap and learn along the way? (assuming you know what you want already)