3-layer ASP.NET app - Need critique/advice
Things I would change in your code/approach:


log errors
get rid of static service methods
hide dll exceptions in ui. Catch it in BLL and log it/do something with it.
change DLL so the method in BLL instead of:


int userId = Int32.Parse(UserDAL.Get_UserId(username).ToString());

would use:

int userId = new UserDAL().Get_UserId(username);

These are first things that come to my head.