A few reasons for me:
1. I've got one 30-gig IBM 75gxp right now, eventually I'll add another one and RAID them - I do a lot of music editing and really want the extra speed for dealing with large .wav files.
2. Easy overclocking - didn't know about the MSI at the time or else it wasn't out (this was a few months ago, and the KT7-RAID seemed to be THE OCing board at the time). Got my Duron 600 running at 935 rock stable, and I could push it higher if I had better RAM.
3. Uniformly excellent reviews at first, although to be fair I've seen one or two since then that take Abit to task for quality control issues.
4. Bought the non-RAID for a friend and it was a pleasure to work with.
Overall, once I disabled ACPI in Win2K, I've been EXTREMELY happy with this board. That said, due to good reviews, a good price, and no use for RAID, my next Duron build (for my sister) will use the MSI K7T Pro2.
-brennan