I downloaded Firefox 3 yesterday. It was slightly rougher than expected, though. Like many people, I assumed that “Download Day” would start at midnight GMT, or even midnight Pacific Time (since they're in California). Turned out it was actually slated to start at 10 a.m. Pacific. Maybe they wanted to have breakfast first.
I'm in the Mountain Time Zone, so it was after 11 o'clock before I attempted the download. The download link was for Firefox 126.96.36.199, not 3.0. Oops! I did some URL hacking and figured out the address to download the 3.0 version. Out of curiosity, a little later I refreshed the page and version 3.0 showed up. Guess someone noticed. Due to the mix-up and a bunch of load-related server problems, Download Day didn't actually officially get started until 11:16 a.m. PDT. I was pretty sure my download started before that, thanks to my hacking the URL instead of waiting for them to fix the home page, so I downloaded it again today to make sure it counted. (They'll cancel any duplicates.)
Installation and setup was another little adventure. With the various tweaks I've made over the course of time to my Firefox 2 install, I wanted to start fresh. So I made copies of my data, dumped a list of my extensions, etc., then wiped Firefox completely off my computer and before I installed the new one. That went fine, but when it came time to reinstall the extensions, I found it difficult since a lot of them are hosted on mozdev.org and it was also having server problems, presumably due to the heavy load. They were able to straighten out the problems after an hour or so, so I've got them now.
Fortunately, since then it's been pretty smooth sailing. Many of the new features will matter only to developers, but there are other changes worth noting. One of the best new features in my book is actually pretty small: Previously, when you submitted a form with a password, Firefox would pop up a window, asking if you wanted it to remember the password for you, and wouldn't actually submit the form until you answer. The problem is, sometimes you're not sure you entered the right password, so you'd rather not make the decision until you see if it actually worked. In Firefox 3, the question appears as a thin banner at the top of the page, and the form submits without waiting for your answer. Yay! Bookmark and plug-in management is better, too, and the new rendering engine seems to work fine.