Of course I swore blind that the new theme couldn't be slower and it was (and still is for IE6 users I know - sorry), but this time I really am sure
What is does mean is that cookie problems (login / out etc) are sometimes cured (and caused) by switching between them as the cookies are domain specific. A cookie sees a difference, but the processors don't. A processor may be dealing with a bit of number crunching for your request, then a bit for another (.com) request, then yours etc. until it has done the work and spit out the results.
Re speed, the good news is that we have the new server which is just waiting for its operating system install and being wired up at the data centre.