This chip is not actually AHCI compliant - I recommend you read the introduction of the spec if you don't understand objectives and roles from this spec. It doesn't imply anything relative to performance or reliability. It means that support by future OS (Linux, Vista and OSX) and interoperability with other Serial ATA components (drives, other chips) COULD be of lesser quality - this depends more on Silicon Image support evolution in time and the maturation of their product interoperability tests.
Interoperability, features and extensions supports testing are currently done by industry participant internally and in plugfest from which no results are published.
Serial ATA standards, extensions are really fragmented and this situation is a total mess for the consumer.
The current state of interoperability between SATA devices is good in numbers of peripherals that COULD work but quite poor in features supported between them (see firmware updates of numerous drives notably the latest Maxtor/nFORCE history) .
For example there are no standard or label validation tests that say Sil3132 supports 3Gbits/s rate (Serial ATA 2.5 tries partly to correct that). It doesn't mean that Silicon Image doesn't do its maximum to make it work reliably at this rate and that Sil3132 doesn’t work at his rate with some drives
Nonetheless it clearly doesn't work (or so say the driver inf file) with NCQ with some drive that say to support it too because of incompatibilities.
For a few bucks, all these things don’t really matter for my personnal use. At work the situation is different: I buy only AHCI compliant controller and carefully qualify the references of my hard-disk drive.