I see cancel is ignored for 3 seconds according to log, look like I need to implement "hard" cancel logic as it may mean single user task lasts for 3 seconds here

Just a note.

Today after working a few hours with this build, it gets quite slow.  It does not matter whether I am editing an entity or not. The IDE cannot catch up with slow changes even if I wait. The red error stripes in the source code gutter sometimes take 30 seconds to appear. Now I get "Uncompilable source code" with COS.

if it's not only for entities it's either some memory issue, may be caused by persistence or some another issue, heap dump may help to evaluate in this case, and snapshot may be too, thread dump may help to to see if scanning thread is blocked someway.
201208150001 may be a bit better with memory usage from persistence side as it do not use new java model and try to reuse already created before. It's better to check/dump/etc with newer build.

At least for me I see some memory problems with 7.2 without any persistence usage, just nb modules and some debug/run and it cause some issues like "can't compile" and cause scanning blocking and cause constant error badges etc. there are number of oom filed already I'm looking for.

Integrated into 'main-golden', will be available in build *201208180001* on http://bits.netbeans.org/dev/nightly/ (upload may still be in progress)
Changeset: http://hg.netbeans.org/main-golden/rev/5098ce51a4ac
User: Sergey B. Petrov <sj-nb@netbeans.org>
Log: #216053, #216827 don't need to reparse annotation mirors as model is already created

May be this can help:
http://statistics.netbeans.org/analytics/exception.do?id=606726

Another one:
http://statistics.netbeans.org/analytics/exception.do?id=606727

Another one:
http://statistics.netbeans.org/analytics/exception.do?id=606728

issues #217066 and #212643 and middle report do not have assigned issue yet.
can't say which one may cause with one issue as root cause, but all may be related.

bht,
For entities edition, do you have slow edition after a long ide rest or after recent edition, on each invocation or from time to time?
How much named queries do you have in total? Fr first entity opening it's expected to have some delay as persistence model is created but it shouldn't happens later, except case if there is not enough memory (may be).

7.2 is always slow with this project. Just a couple of files open is enough. I have about 60 entities with perhaps 30 named queries in total. Once I opened 2 copies of the same project because I was working between 2 different versions. But one copy is slow, too. The IDE gets 800 MB Memory which it all used at some stage and the PC has 3GBytes.

60-30 shouldn't use much memory for jpa model, for me it's about 10 mb for about 300 simple entities+800 simple named queries, thanks, 
it's likely isn't the reason for latest builds but may be for 7.2.

http://hg.netbeans.org/web-main/rev/e515274a3c8c this one change should make calls to suspected slow Elements.getTyeElement from jpql validation extremely rare now, may be none calls will be made in most cases.

I still can't reproduce the issue neither with maven nor with a lot of entities/queries so have to iterate in fixing.
As snapshot for this issue contain affected calls, please try a build after mentioned above fix integration.

set as fixed for more evaluation as provided snapshot(with 4 long Element.getTypeElement) shouldn't happens any more in most cases. please reopen with new one if it's still the problem.
Also, have you tried to increase XMx? I have max heap at 390 mb with 3Gb memory if set automatically and it's not enough is I'm working with several nb modules and debug/cc etc. Usual level I have it about 300mb but jumps temporary up to 700(and back, suppose there is no memory leak) and if Xmx isn't set it may case oom, slowness etc.

Closing - possibly fixed because there is no other negative feedback from reporter.