Paint.COM is fine with me, although if you're losing users over the name, of all things, i think it might be a good idea to change it.
I was thinking maybe just RealWorld Paint to keep it simple. Dropping the .COM might reduce confusion between Paint.net and Paint.COM.
If you want to make it not sound like MS Paint, then maybe RealWorld Paint Pro will help say this is a professional program?
My two cents.