Well it all depends on what your set up is and how many
connections you have etc. etc.

First step - use the JMX interface to turn on stats in Jetty
and then have a look and see what is happening.

Try things like:

+ increasing maxThreads so you have more threads to service
requests

+ Increasing minThreads so low resource action takes place earlier

+ Decrease the idle time so you have less idle threads consuming resources.

+ Decrease the low resources persist time so that when you are low on threads you don't persist idle connections too long.

+ Look for stuck requests. Do you have some servlets that
are taking tooo long to complete. (you have pre compiled your JSPs right?)

+ Stop using JSPs :-) only joking

So I expect that it is just tuning, but it may be a bug.
The stats will tell you what is happening.

IF it is a tuning issue it is not hard to optimize it
or you can cuy a Jetty support contract and we'll tune it for you http://www.mortbay.com/mortbay/services.html