I know I didn't hit the tip of the iceburg there. I just named a couple.
Also I agree with you B and STRONG is stupid but it's targeted for those who can't remember that B stands for BOLD but it's besides the point that STRONG should have really called BOLD if we were to argee having it. I guess it's targeted for the newbies. Who knows.
As far as error checking, I combine my error checking client side and server side. Any security stuff would be server side but it's nice to remind the user that they forgot to fill out a required field without them having to submit the form and get it back.
