LISTEN / NOTIFY performance in 8.3

Hi,

I'm noticing a strange increase in the amount of time it takes to
issue a NOTIFY statement.

I have an existing app that provides a producer / consumer type of
queue and that uses the LISTEN / NOTIFY mechanism to signal the
consumers of new items arriving in the queue.  The consumers then
process these items and issue a notify to signal that they have been
processed.  In the past issuing these notifications happened very
quickly, now on 8.3 I'm seeing all of them taking over 300ms and many
of them taking 1500ms or more!  The notifications are happening
outside of any transactions (which is itself a probable area for
performance improvement, I realize) but I'm wondering what might have
changed between 8.1 (the version I was using in the past) and 8.3?

TIA,
Joel