It's funny: The newer boards aren't better, just cheaper to produce. And they cost more, because they're newer.
The 865/875 chipset series was released over 1.5 years ago. There's no room for improvement: there haven't been any technological breakthroughs since. The 915/925 chipsets were released since, supporting PCI-Express, but still no improvements. The old ICH5R southbridge was replaced with the ICH6R, but the only thing of note there is that they went from 4 PATA/2 SATA drives to 2 PATA/4 SATA drives.
Some boards have been updated to Firewire 800 from Firewire 400, but Firewire 800 isn't even new, and it's not properly supported by Windows XP (defaulting to lower speeds). So Firewire 400 is fine.
The IS7 has 5 analog audio ports, rather than 3, so you can have 5.1 sound off the analog ports while keeping your Microphone and Input connectors usable. Most other boards give you 3 analog ports, forcing you to electronically switch your microphone and input ports to output ports if you want 5.1 analog sound. The IS7 also has digital coaxial sound input and output, rather than just output as most other boards. The IS7 is also laid out with the AGP slot in the top position with the 5 PCI slots in the lower positions, leaving an empty space between AGP and PCI-1 for additional cooling or double-width card coolers without sacrificing a PCI slot as you'd have to with most other boards.
The IS7 is the cheapest high end board to offer ICH5R RAID and Firewire.
Abit is pushing the newer AI7 as a replacement for the IS7, but it doesn't have all the features of the IS7, it would appear to be cheaper to produce, and it cost more because it's newer. The IS7 is the better board in many respects. It won one of Anandtech's "Best Board" awards a year and a half ago.
Many of my associates use the IS7. Unfortunately, I bought the Asus P4C800-E Deluxe because it was recommended by a certain RAM company, and I was doing a RAM review. After a month the CPU voltage fluctuations were so great I gave up using the board (I could no longer overclock with it). I looked up much user info on the P4C800-E, and found the entire line of similar boards (P4P800/P4C800, all versions) were comming up with the same problem. I reported that in a board review at Sysopt.
Having found the P4C800-E Deluxe to have a defect (Even Tom's had to fix their board, but they kept it on the down-low), I'd also received a Soyo P4I875P Dragon 2 Version 1.0 Black label, free for review. Since it was free and didn't have the problems of the P4C800-E, it's the board I'm using now. However, if I had to buy another board, I'd go with the IS7.
I've put somewhere between 50 and 100 users on the IS7, and I've heard very few complaints, and those complaints were centered around interference issues with the onboard audio. Most were resolved.
<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>