I lost all interest in parking programs the day Parking Company of America told me that my 2 completed punch cards for 10 days free each were now almost worthless in their new points program. I fired them: I have never used them again.
I now park with Expresso Airport Parking, which has the lowest rates and which makes no promises about future benefits.
Parking programs don't need a forum. They need a thread warning our members that those programs are often managed without integrity.
The family near LHR I found through parkatmyhouse.com several years ago has been awesome.
Prior to that, I used LHR parking and, once, Purple Parking...it only took one use (and not even my own car) to make me realize I was not going to use them again.