Limiting the summary buffer by recipient

[address expires 29 Jan 2005]

I have recently switched from RMAIL to gnus for my email, and am using
the nnimap back end.  In general, I have been totally delighted by the
host of new features offered by gnus.

However, the one thing that seems to be missing is restricting the
summary buffer by recipient.  In RMAIL, this was just M-C-r.  I'm
afraid I got fairly addicted to that feature, as I store all of my
sent mail in one big mail folder and then like to search it by
restricting the summary buffer to particular recipients.

Is there any way to achieve a similar result with gnus?  I've set the
following in my .gnus:

(setq gnus-extra-headers '(To Cc))
(setq nnmail-extra-headers '(To Cc))

and tried to use "/x", but it doesn't seem to work.  I'd be grateful
for any pointers on how to get something like RMAIL's M-C-r if this is
possible.

Thanks,
David