Only noticed anything the last couple of days but it is gone now. With this being a beta site, and new features being added I used to notice changes and slowdowns periodically, but found that these 2 free browsers run smoothly through almost anything while the ones I used before would suffer at different times for each. There have been other technical discussions in the past using the word slow or in the technical section, with different suggestions in the answered questions and various tips, that may be worth a look. The number one problem for me was whenever there were large automatic downloads of software updates in the background that slowed everything down on all websites that are complex. If I checked and lots was downloading in the background - your received numbers were constantly changing and going up even when you did nothing, it helped to make sure it all downloaded before turning off the computer even if it took hours, otherwise it would start all over again every time it was turned on.

The new Chrome may be even better than Safari has been for speed.
Google Chrome http://tools.google.com/chrome/
Safari http://www.apple.com/safari/

It has actually gotten much better for me this past week. I was getting all kinds of script errors and freezing, but now its awesome for me.

The Devs are doing some work on the site tonight, mind the hiccups if you experience any.