8.4 is a medium-sized release. The largest change is a ground-up rewrite of one component in the accounting code. Accounting changes always make me nervous -- clients get very unhappy when there are problems in financial reports -- but this set of changes has been live on two client sites for a while because it fixed critical bugs for them, so the code's been tested and is very likely solid. Launching 8.4 is nice because, since everyone is now using the new-accountant code, we'll have one less branch to worry about.
The Mailman upgrade is relatively minor. I wanted to change the return addresses from listname-bounces to listname-lists, because some MUAs display the return address and the -bounces scares naive users. Since we would be updating code anyway, I also wanted to continue tracking the current Mailman 2.1 release.
Those of you who follow my Twitter account will remember I was struggling with optimizing certain slow SQL queries. That work made it into 8.4. I compared the output of searches with 8.3 and 8.4 and was depressed to find that the result sets didn't match, but eventually realized that the 8.3 queries were subtly wrong and would occasionally return records that weren't supposed to match, so the optimization turned out to be a bugfix.
We also concentrated on catching up with client requests, which had been accumulating for a while. Not quite every request made it into 8.4.0. I have a few dangling requests on my list that couldn't get done in time and must wait until 8.4.1, but the list is certainly a lot shorter.
Today I do the usual post-launch thing: go into work early to check the exception e-mails and to be there in case clients make any panicky calls. For some releases the following week was a really unhappy one, with lots of urgent bugs pouring in, but the 8.3 release was a really quiet one; IIRC, the few bug reports that came in were not related to the recent launch at all, but were long-standing issues that someone had just noticed. The accounting changes make me think things won't be that quiet, but I'm still optimistic.
And then we can start thinking about 9.1!