I have had zero problems using Serrillel2 adapters on the ICH5R-controlled ports on my DFI LanParty Pro875 and IC7. I am currently having zero problems using them on the VT8237-controlled SATA ports on my GA-K8VT800M (Gigabyte Athlon64 board with Via chipset).
You can't run optical drives, or use hotswap, but for running ATA100 and ATA133 hard drives (I don't believe ATA66 and below hard drives are officially supported), they're fine.
You'll also see a performance boost, not because of the "SATA" nature of the connection but because your hard drives will be masters of their own channels (As opposed to sharing PATA channels amongst themselves or with optical drives), and the IDE channels will not have to go through a relatively low-bandwidth PCI bus (which is what happens when you use a PCI hard drive controller).