I just updated from Jenkins 1.505 today as part of resolving another outstanding issue. I notice that the main dashboard page is much slower to load than it was before, and also notice that the server gets high CPU load in the process (it gets super-bad if you try and reload it a few times, as one might do when a page seems frozen). This is not the case on the individual job pages, the "manage Jenkins" page or other such ancillary pages.
My main page has quite a few jobs in the main view, but that didn't have an adverse effect before.
It did have some trouble connecting to the slave, right after the update, but that appears to be working properly now.
At the moment, several minutes after it seemed to have normalized a bit, I see one CPU is now completely spiked by Jenkins.
Downgraded to 1.505 + git-client 1.03 until this is resolved or explained.
Note 1: After the downgrade things are back to being speedy. The dashboard loads quickly on opening it or on switching to it, and any CPU load is very brief (versus waiting several seconds for the page to display, or much longer if it was refreshed a few times). I hit reload several times in succession... it was reloaded in a second with no major load on the CPU (versus waiting around 30 seconds for the page to finally appear on the newer version).
Note 2: Even in 1.505 you end up with one Jenkins-bearing CPU that stubbornly spikes at 100% after a few quick reloads... and appears to stay that way (if you reload a few more times you still end up with this condition, though it might be on another CPU in the system). So the persistent CPU spike may or may not be related to this issue.