Ideas...

I think something is going on with ST, I tried to log in, recieved a session, but it's malfunctioning... i seriously hope you aren't live updating code while running beta tests.. but if you are...

Also, I emailed you more comments... Here they are.

Basically, a few things you should think about, if you aren't already using them... Once, decrease the sizes you are sending out... alot of the time javascript can be condensed from 20k to 3k with just some simple encodings and a script that will decode the rest. Sure, it may increase times on the other end, but that usually isn't very long, unless they are working on sub pentium 4 levels. Same with the CSS, you have to remember that when people are accessing files, they are actually downloading them, so removing all whitespace and new line chars, will decrease on the meta content, and 20,000 unique hits later, you save 200k in bandwidth..(in a perfect world). but since your sight is using heavy .js you will find it is faster to condense you .js. Take a look at http://www.dhtmlgoodies.com , they have a very impressive suite built inhouse. when you DL is you will notce two versions of suite.js... compressed, and uncompressed. The client sees the compressed verion, like 29K! uncompressed that balloons to much much more. Oh, and not just white space. javascript does not need any ;'s. Which will easily cut your code by 5% of size.
Your using php it looks like, so you will also want to use some things like a cache. You could easily, set it up on peoples account where things like what they have already seen are just referenced onto the database. This can then be used as a history tool, in case a friend of there changes there own history... the account will still have the info, and it can be grabbed faster, and easier from a ST db. Use a mysql Cache and you will probably want to use something like SMARTY templating. Because the caching features are very useful. A PHP cache is very good too.
I'm sure you have glanced over some of this stuff before, but from the looks of you .js.. you really should remove all comments, white space, and ;'s (chances are it shouldn't break anything), and newlines. Then at the top, reference the uncompressed files with a link in th comment so that all legal areas are covered too (usually sufficient, check with your sponsor).
use AJAX a bit more too... i noticed too many full lifestream(?) refreshes when playing with name changes.

hope this all helps