I'd recommend Leopard over Tiger too. I've been using it fine on my iMac G4 (1.25GHz, 768MB memory).
The one thing about Linux on iBooks and PowerBooks is that getting the battery status to work is a hassle. Other than that it's fine.
My only disagreement with you here, is yet again Tiger.
The OP of course will do what he wishes, but you and I have a big difference in opinion about Tiger it seems.
Although I might suggest iStat Menus over Menu Meters. But that's a personal preference kind of thing.
iStat, IMHO, does about the same thing as MenuMeters, but is a little more system-heavy, and a bit messier in displays. It gives those little menu panels, instead of just dropdowns, and I don't recall if you can configure it as much as MM, but either would work, and are
very useful in conjunction with Process Wizard.
As to Tiger vs. Leopard, I think to comes down to use dependency. Your main problem seemed to be SMB, with W2K3. I find both suitable OSes

I even run Panther on G3 and G4 systems, when I want a very lightweight OS. One of my complaints about Leopard is that it killed some very valuable extensions and prefpanes that I run in 10.4. Again, that is use-specific.
I can tell you that there are quite a few tricks that I can pull off in Tiger that are simply impossible in leopard, however, if you want to use MacPorts, or Brew, then Leopard is better.
One oddity that I noticed in Leopard is that, while Terminal now supports multiple preferences for views, it often doesn't save changes on exit. I never had this problem on 10.4.x, and I'm rather obsessive on the appearance and colours in terminal, using an old, green or amber, monochrome theme, that I find relaxing to my tired eyes, over black on white, or white on black.
I also see less RAM usage in Tiger, but I expect that if you reconfigure Leopard, it can behave. I am a bit shocked that you had it running on a 400MHz TiBook, which is a
tad impressive.
You may want to contribute some pointers for how to configure Leopard in a slim mode, or if you wish, send me whatever you have on the subject, and I can turn it into a column for easy reading.
One of my personal favourite prefpanes for Leopard/Tiger is Shapeshifter, which I believe breaks in Leopard, although I can't say with certainty. Perhaps it was just that my custom theme didn't work in Leopard, or some other reason that had me stop using it on 10.5. I do prefer the dark theme that I use, over the glittery, basic Aqua theme, as it is far more subdued.
I'd recommend Leopard over Tiger too. I've been using it fine on my iMac G4 (1.25GHz, 768MB memory).
The one thing about Linux on iBooks and PowerBooks is that getting the battery status to work is a hassle. Other than that it's fine.
Is that still a problem with Ubuntu 10.04 LTE PPC, or YDL 7?
For the record, you can often do a great deal of cross-system compatibility with
port,
brew, and
git, especially if you
install gtk2 +aqua+no_x11, to use gtk in native mode.
As long as you don't mind compiling, you can port most Linux programmes from src, to work on PPC OSX, instead of PPC Linux distros. The GCC compiler for OSX, does work.
You can even run Gnome / Nautilus in parallel to OSX Aqua / Finder, by using these tools. This allows you to compile and use some more recent software, although dependency trees, and kernel extensions can give you a hassle.