Okay, first of all, this interface is incredible. Second of all, buy it.
For the price, there is no other interface more logical, pure, or straightforward. The most channels I use at once is maybe 16 or 20 (for a big kit), and I didn't want to have to get an 8 channel interface and then stack expansions on top with digital lines. I thought, hey, look at the 24io...what a great idea. Come to find out, I made the right choice absolutely. I was able to tell a difference in quality immediately. Clearer and crisper in playback, and BEAUTIFUL in recording---the converters in this are just astounding.
I've been a PC user forever, and I don't use ProTools, I use Nuendo. I have a small PT8 system to mix certain client projects, but I prefer to record and mix in N3. I have worked on all kinds of systems, Mbox, 002, 003, Firepod, Delta 1010, EMU, and others, and this is by FAR my favorite. I was looking for good sound quality without all the crap--the digital lines, the preamps, the fancy knobs--I use high end analog preamps and other outboard gear, and this solved all my problems.
Now, the only con (and the reason for the 4.5) I have is that it's a bit tricky to figure out the difference between your PC sound (like if you play songs through iTunes) versus the sound you use for your DAW. What I had to do was use outs and ins 23/24 for my computer sound. A bit unexpected, and maybe I just didn't look into it that much, but still fine. I'm guilty of not looking through the manual adamantly.