The bottom line here is that in the vast majority of cases, slowdowns (where a page takes more than a few seconds to load) are usually a problem with a user's own internet connection or computer. And they're usually transient. That's why you see a few people saying it's slow and some people saying "it's fine for me" and indeed, thousands of people not saying anything at all because it's fine for them too.
You might like to try downforeveryoneorjustme.com/ which will tell you if Mumsnet (or any other site you care to test) is really down or if it's just you.
You can generally tell that it's not the server being slow to respond if you start getting something and then it slows down - the server has done the heavy work of generating the page, it's just the download that's slow.
As to the suggestion that Mumsnet is overloaded, the server is actually fairly lightly loaded most of the time. We monitor the load on it continuously so we know how busy it is. Once in a while when some big indexing process or a big mail shot is taking place it can get a bit bogged down, but generally it copes just fine. And the network infrastructure (bandwidth, routers, switches, firewalls, etc.) is fine too and serves sites that are much busier than MN.
Since the original Tech escaped NikitaTech has been having to get to grips with over 1,000 files of Java, a few hundred templates, dozens of third party libraries, a CMS system, PHP for blogging, and a hundred or so shell scripts that tie it all together. This means that some changes that should be relatively easy might take a bit longer. She's doing a stirling job though, fixing all kinds of stuff.
There are a few things we can do to speed up some pages, but they're pretty minor and won't make much difference. The talk pages are already not rendered as one big table but as a series of DIVs, so the browser can display them as they come. Allowing browsers to cache the DWR javascript is more complicated than it might appear (the library that provides it generates it dynamically and sets the headers), but we'll get to it eventually. Things like compressing Javascript messes up some browsers, minifying breaks some Javascript that isn't perfect, and so on. In an ideal world we'd do all those things and more...
Whilst we're at it, the various mentions of crashes on this thread and elsewhere are actually mistaken - the weird messages that were reported are actually just us releasing a new version of the software; fixing stuff, improving stuff and so on. When the new files are deployed (now fully automated) it takes a minute for everything to straighten out, caches to reload etc. We try to do most of them late at night, but if it's urgent we sometimes do them mid-morning.
Oh and for the record, in the "pls ignore" thread Nikita wasn't learning how to post; she was testing a complaint that the indexing process (flippin' complicated thing that it is) was knackered. The original intention was to delete the thread after a few minutes, but it took on a comical life of its own so we left it there.
Hope this has cleared up some of the points raised. Feel free to post more on the topic - someone does read it all and we often work on stuff even if we're not posting about it, because I am sure for most people the technology behind Mumsnet is pretty blooming dull!