Hey all, thanks for the responses, especially Kata's and Tiger's. One piece of advice I follow is to always email the provider and ask a question, even a dumb one (maybe especially a dumb one). Then wait to to see if and when it gets answered.
My current hosting provider answers even dumb questions politely and quickly - usually within 30 minutes.
the other hosting company.co.uk answered my dumb question after 3 days.
the other hosting company.com have not yet answered my not dumb question (I can't complete their registration form, because it doesn't allow a UK postal code). It's only been 24 hours though
lunarpages answered my dumb question within an hour and politely too.
Another thing I look for is a message board hosted by the provider with an active and friendly user community. My current provider has one. Lunarpages has one.
Hmmm. I seem to be talking myself into signing up.