The first thing we have to make note of is the fact that the performance decreases that we saw in the last driver set from ATI seem to have been fixed. Apart from this there isn't a whole lot else to the driver. The additional functionality on offer in the Catalyst Control Center as far as Overdrive goes is nice and is great for people who don't know or don't feel comfortable in manual overclocking.
Also included are a few fixes under a number of operating systems which is always a good reason to upgrade. We'd also recommend that people move to this official driver if you're using a HD 4890.
The 9.4 driver set on a whole is pretty good and there's really no reason not to upgrade from the 9.2s. In the event you did install the 9.3s, though, we would recommend you upgrade immediately.
As usual, we can't cover everything, so if you notice anything particularly interesting with these latest drivers then jump into our forums and let us know.