Another manufacturer's previously-installed SATA driver may be accessing a Sonnet SATA card in error causing a drive access slowdown. For example, we have seen Fusion D400QR5 performance drop from 200MB/s to under 50MB/s in such circumstances. The solution is to remove the other manufacturer's SATA driver.
Sonnet has isolated the occurance of drives not mounting in 10.7.4, which occurs only in 32-bit mode with the Tempo SATA E4P, E4i, and Tempo SATA Pro ExpressCard/34. Users running in 64-bit mode will not experience any issue. (To boot in 64-bit, hold down the 6 and 4 keys when the Mac starts up.) Install driver 2.2.9 or greater to fix the 32-bit mode issue.