Flash, php, and mysql

Hey guys, I just wanted to know what your thoughts where about database driven applications using this technologies?

I wanted to know about:

-Security: Is it possible to program secure enough flash database driven aplications ?
-Speed: Is it possible to program fast enough applications, when millions of users are login in etc?
-Robustness: what can I expect as far as errors, for example in inserting information to databases through flash, or is that soemthing completely independent from flash.

Something else I would like to know, is how do other technologies compare and if there are any advantage in using for example ASP, or other databases. I ask this because I have noticed some high profile flash sites using ASPX for their database driven sites. Wallop.com is one of them, and I wonder if there is any reason at all, any advantage on using asp.

Any information will be greatly appreciatted, as always !!!