Hard to say. It's fairly common for AD/DA chips to be dropped or replaced with higher performing ICs by manufacturers, so it's quite possible the circuitry has been updated.
I bought the iMic first but soon replaced it with a "real" ADDA converter after I realized it's limitations (it's quite audible in A/B comparisons with the source program material). It took a few devices before I finally settled on one; unfortunately it cost me $ 750 before I found one that had the performance I needed. These days the better FW and USB devices are good, so if your needs are critical you won't have to spend as much as I did.
The iMic (original) was adequate but hardly perfect, with in particular a rather lazy, rolled off high end and rather poor bass response (red=line in; blue= mic in). In it's defense, it's a rather good curve for spoken voice recording, but not for serious audio use.
Compare that to Apple's built-in audio (eg: PowerBook G4). An improved chip in the iMic would be welcome news.