I have visited Bangkok and Pattaya a few times but have been out of the scene for a few months due to a few issues.
Anyway I am a UK Passport Holder and in May I will be entering using the 30 day visa exception. Now my situation is that I will be entering Thailand for only one day/night and then I have to fly to a nearby country for a one week business trip, then I fly back and will stay in Thai for two weeks, is this kind of re-entry allowed? The whole trip comprising two entries will be less than 30 days.
I think you already have your answer but just to clarify. The fact your whole trip is less then 30 days is not relevant. Each entry will be done under the Visa Exemption scheme and you get 30 days each time. There is no issue coming back a week after you left and entering under a Visa Exemption again, lots of tourists who travel around South East Asia do that as Bangkok tends to be a gateway airport.
I'm not sure wikipedia is accurate when they say the Visa Exemption can be used an unlimited number of times as long as you arrive by air. I think they will look at your travel history and if it looks like you are using repeated Visa Exemptions as a way to stay for an extended time in Thailand you will be challenged. I forget what the final conclusion was but there was a discussion on PLB about this very subject. For guys who just come a few trips a year it isn't an issue for sure.