After axely's endorsement of xfs, I decided to try it out on this machine, with a setup similar to what you see near the end of that post. Root and home were switched to xfs, with an ext2 boot partition and standard swap; the system was built from a server installation and without a desktop manager.
Boot and load times were similar to ext3 with dir_index enabled, but lagged by a second or two. I blame that again on the file system load being shifted to the processor, when (as I understand it) ext3 is less cumbersome.
Either way, xfs was a far cry from standard ext3, and required far less tweaking to set up than ext3 with dir_index, journal writeback and noatime. Just for fun, I used it on an Xubuntu dual boot on a dual 2.8Ghz Xeon machine with an Ultra SCSI setup. It's alarmingly faster than Dapper's default ext3.
So thanks to axely for pointing this out. Cheers, friends!