extreme erc slowness

I'm using ERC 5.2 on Emacs 22.

I've noticed a strange problem with ERC.  I connect to a server, and
ERC will try to join all my channels.  When I do this, ERC takes 100%
of the CPU.  Emacs becomes unresponsive -- occasionally I can C-g to
stop whatever it is doing, but this only works randomly.

Sometimes this problem lasts long enough for my other ERC connections
to time out.  So, these disconnect, then reconnect, prolonging the
problem.  Today this went through two rounds 

Any clues as to what this could be?  Or how I could track it down?

Tom