The real problem is the "audience" they attract with such petty offers. It's unlikely a truly frequent flyer, or even an infrequent but high dollar flyer, is likely to spend any time completing a survery -- any survey -- for 25 points (which have a retail value of $1.00, and probably an internal value of, I dunno, maybe 5c.)

So you have a self-selecting sample that probably represents only the most frugal flyers, that have lots of time on their hands. How valuable can that be?

Here's my table of values:

3 points - huh?
10 points - pardon?
100 points - open 1 eye
250 points - open both eyes
500 points - yawn
1000 points - operate pen or pencil for a maximum of 60 seconds
2500 points - answer phone
5000 points - complete survey - maximum 3 minutes
10000 points - complete survey - maximum 10 minutes
25000 points - complete survey - actually pay attention to questions
50000 points - give undivided attention - during work time (30 minute max)
100,000 points - give undivided attention - during meal break (60 minute max)
250,000 points - supply actual thinking