Has anybody clarified exactly what period of time must elapse between exit from thailand on a visa exemption and entering again on a visa exemption?

I am a frequent, genuine tourist to thailand, maybe 4 or 5 times a year for periods up to 30 days.

There is no set period.  It depends on whether the immigration officer thinks that you are abusing the visa exempt system.  Another "up to them" situation!

Edited August 14, 201412 yr by wayned

The only thing mentioned in the guidlines immigration on entry should be using is in reference to doing a in/out visa runs after staying for the full 30 days. The word immediately returning is used for them.

If your enteries are speared by a few days and you did not stay the full 30 days you should not hav a problem. If separated by weeks after staying the full 30 days you should never have a problem.

For short stays you should never have a problem.

Make sure you have a return ticket and a hotel confirmation, just to be on the safe side.

And what if you have a 30 day visa exempt entry that you extended by 30 days (after 29th).  Any ideas if that's going to raise a red flag for some strange reason?

Why would it be a red flag.

I suspect they would frown upon you getting the 30 day extension and then doing another 30 day exempt entry.

If you wanted to stay longer you should get a tourist visa.

The 30 day extension of a exempt entry is meant for those that have had a change of plans and want to stay longer.