I use "XXX" too - usually in the form "XXX FIXME".
Timing is everything, especially in humour...
I nearly choked on something when I realized this thread was going on as I read notes on the PostgreSQL list where the somewhat famous (?) Tom Lane observed that he was planning to comment a commit to password management code with "XXX FIXME"
:-) :-) :-)
So this is clearly an idiom still in active use!!!