I wonder, as OME suggested, it is also:
4. a great social site for like-minded aviation enthusiasts.
5. a fantastic forum where aircraft builders encourage each other and share valuable ideas and techniques.
?
I also believe that, for less than a dollar a week, getting a first class membership is worth considering for those who have not thought about this yet. Fifty dollars per annum is money well spent.
Regards,
eightyknots