Comments about 'Keystone' for internal ticketing

We have been using Jitterbug for a while for our ticketing system - but
have quickly outgrown it - and seem to have a need to move onward to a SQL
based set-up - I've been looking at a few and have started focussing on
Keystone - anyone using it and have some comments good/bad/creative re:

please hit me off-list...