OK, I decided to do some pre- and post-update "benchmarks". Note: I have adblock plus installed, so that could affect my results.

Pre-update:
Time from clicking "GMail" in bookmarks to gmail loaded:
1 minute, 11 seconds

Javascript benchmark test (http://celtickane.com/projects/jsspeed.php):
Try/Catch with errors: 1547 ms
Layer movement: 5361 ms
Random number engine: 5809 ms
Math engine: 8973 ms
DOM speed: 7003 ms
Array functions: 614 ms
String functions: 279 ms
Ajax declaration: 1578 ms
Total Duration: 31164 ms

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Post-update:
(Note: components listed Adblock plus as enabled, but I didn't get the button in the lower right hand corner, so it's hard to say -- some of these results could be skewed by that -- also, visiting sites with ads that used to be blocked, the ads showed up, so adblock plus did NOT seem to be loaded... sorry guys, should have forseen that)
Time from clicking "GMail" in bookmarks to gmail loaded:
46 seconds

Javascript benchmark test (http://celtickane.com/projects/jsspeed.php):
Try/Catch with errors: 1606 ms (+59 ms)
Layer movement: 5842 ms (+481 ms)
Random number engine: 5038 ms (-771 ms)
Math engine: 8689 ms (-284 ms)
DOM speed: 5530 ms (-1473 ms)
Array functions: 784 ms (+ 170 ms)
String functions: 679 ms (+ 400 ms)
Ajax declaration: 1882 ms (+ 304 ms)
Total Duration: 30050 ms (- 1114 ms)

Overall, the results are pretty over the board. The most drastic change seemed to be in loading gmail (could be a result of adblock plus), and DOM speed (down almost 1.5 seconds!). However, I would say that there does seem to be a general speed improvement. However, I just tried to visit digg and the browser crashed.