portknocking with pf?

[Kory T]

I'm sure portknocking has been discussed in this list before but has 
anyone actually tried it with pf?  At first I didn't think it was a 
good idea since the patterns can be sniffed until I viewed the whole 
concept of it on portknocking.org and the example perl source they have 
on their site.  I think this would be a great additional feature to the 
openbsd pf if implemented properly.  If any of you have tried this or 
don't think it's a great idea let me know your opinions.

Kory