I just installed the new MintPPC 11 and have been playing around with it, so this is more a quick look than a comprehensive review but I like what I see.
First, the authors announce this is based on Debian Wheezy (testing) so there are likely to be some bugs. This is roughly equivalent to what Ubuntu does, basing their releases on the "testing" branch rather than "stable". The advantage is you get newer versions of software like Iceweasel 7.
I can report to you that Iceweasel 7 is fast. Like super-fast. Another very cool piece of software installed by default is Minitube, a youtube viewer for PPC users lacking flash.
The install was hassle free. The only head scratcher was when confronted with a screen asking you to choose which kernel. I chose version 3 since it was highlighted by default. I thought, "Well, I'll probably break sleep with this, but what the hell? Latest and greatest, right?" And predictably, sleep doesn't work. Other users report sleep works fine, so maybe they went with the safer 2.6 kernel.
Setting up wireless was pretty painless. Sound began muted, but I just had to untick the mute box and had sound working. The LXDE desktop was slick and its memory usage was low. Everything runs comfortably in this iBook with 256 MB of RAM. MintPPC installs by default a variety of of useful software, so everything's there pretty much set up for the average user.
One last thing, unlike the stable branch, mplayer from testing now works on G3's. The stable version was compiled it appears for G4's only. However, VLC still breaks when playing video. I got the stable version working by compiling my own, but I haven't gotten to that here yet.
So give MintPPC a shot. If you're new to it, just register for free at their website and you'll find install instructions and a responsive forum area. Good luck.
UPDATE: If you have a dual boot system, beware that the Debian installer MintPPC uses can corrupt your OS 9 drivers making your OS 9 partition unbootable. The solution is to run Drive Setup from a Mac OS 9 install CD and update drivers. I wrote about this earlier here.