There are various "png optimizers" out there of which to my knowledge "pngout" used to provide the best results (it has been some years since I actually compared those programs). It isn't open source (which is a pitty) but at least it's free software. Ken Silverman (the guy behind the Duke Nukem 3D engine of the '90s) wrote them and releases them for Windows. A friend of him (I think) ports a lot of his work over to Linux, dito for pngout. The cool thing here: He also provides binaries compiled natively for FreeBSD which is certainly cool!
I used that tool to optimize the big PNG files that are used on the starting page. Actually I did that last year but then forgot about it. Now I've run across them again and even if 11.0 is not too far away anymore and will certainly have new pictures (btw., does it have a codename, yet?) IMO it makes enough of a difference to use the optimized ones until then. And of course I can optimize the new ones when they are ready, too. It only takes a bit of trial and error, not too much time. Currently all 7 pictures together are 9.3 MB in size, the optimized versions save about 540K. Altogether it may not be that much but then again half a meg out of less than 10 is not that bad, either. And we're talking about the web here with "time to render" and stuff like that. BTW: Google tools rate our site with 48/100 for desktop and even 39/100 for mobile!

@Eric: I uploaded a file called "optimized_pngs.tar" and put it in /root on the Canadian server as I didn't know where the files needed to go. Could you take a look at that? Oh, and ASX asked me a while back to register for an account on the website backend which I did. But obviously I made a typo on that day and cannot log in. In fact this may be a good thing since it made me try password recovery - only to find that it is probably configured wrongly: It says that it sent a mail (I tried this out a couple of times on different days) but nothing ever arrives. Could you just delete my account by hand and I'll recreate it?