The reason why very few people purchase the TUA266 is that because of the architecture of the Pentium III, combined with its lower speed system bus, it is unable to take advantage of the additional bandwidth offered by DDR SDRAM.
As such, DDR SDRAM offers no performance gains on a Pentium III platform: it will be the same speed as a standard SDRAM system.
In regard to the ALi Aladdin Pro 5T chipset, there are no real issues, apart from some problems with ATi Rage 128 and Radeon video cards. These issues were fixed with the latest ALi chipset AGP drivers.
I didn't say "don't get the TUA266"; simply that it is not my first choice. It's not a bad board, and fine if you don't expect too much from it. The onboard C-Media sound is passable, but an SBLive sounds better.