Slacker, yes, I do have an extra disk controller - an ATA133 one. All working at 153Mhz FSB without problem:
2 LinkSys LNE100TX 4.1 10/100 Ethernet Network (I sometimes use machine for routing, I have two Ethernet adapters.)
1 Matrox G550 Dual Head 32MB AGP video adapter (4x AGP mode)
1 Maxtor / Promise Ultra133TX2 controller. This came with a retail 80GB Maxtor 7200 RPM drive I am using. I reflashed it with Promise firmware so I could install XP on it. I have my hard drives off this controller, cdrw + dvd off mainboard controller (each device is on unique IDE channel, 2 hard drives + 1 cdrw + 1 dvd).
1 Creative Labs Sound Blaster Live (just a basic / cheap one)
One problem board:
1 Antec PCCard / PCMCIA controller interface
The PCMCIA to PCI adapter works fine for my Orinoco wireless 802.11b adapter, but if I try to put in any CardBus adapters it locks up machine. My IBM Firewire PCMCIA card is an example of a problem card. No big deal, as I really wanted the wireless Orinoco card and that is working. From what I gather, the problem with IRQ sharing of PCCard on a desktop isn't unique to my system... there are just drivers out there that don't share well.
I've had three-way routing (both Ethernet + wireless) going, DVD playing (full screen 1280x1024 PowerDvd), rc5 cracking, file copying over network all at once!
The Maxtor (Promise) ATA133 controller - personally I would rather have a Promise ATA100 - I've worked with those in the past. The ATA133 wasn't recognized by Windows XP Professional, so that was why I flashed it with Promise BIOS. I guess the Maxtor "flavored" BIOS on it wasn't matched by XP. My experience with the ATA100 version was that it worked fine, even with older products like Win2K.
The LinkSys LNE100TX network cards are great. I use them in all my OpenBSD routers and so forth, they are "clones of the Digital Tulip chipset" and are fast / efficent. I did try a LinkSys LNE100TX v5.1 (newer revision that just started showing up in stores), it worked fine too... but just for consistency I put in matched set of v4.1 adapters. I see no reason why the 5.1's wouldn't work. I've tested them to 155Mhz, not sure how high they go...
I'm still getting a few kinks out, but the system has been rock solid. Once I quit using the onboard audio, there has been no reason to reboot. I also put on an updated driver from Promise that cut my Windows XP Pro boot time from about 1 minute down to about 15 seconds (after BIOS POST completes)! I thought the 1 minute was just normal - that it was taking a long time to boot because of my three network adapters... but now I know it was the Promise drivers. 15 second boot time is really cool.
USB: I haven't had much use for it yet. I did hook up my compbo Firewire / USB1.1 external drive just to test it... it worked fine off the USB. I plugged it into the "2nd set" of USB that comes with the p4s333, I didn't try it on the "primary set" next to the keyboard/mouse (I don't expect any problems). I run my keyboard and mouse off the PS2 ports, mostly because I had some extension cables handy.
I haven't played with suspend much yet, I will when I get a chance. This system is in my RV (my wife and I fulltime RV, only our 6th month on the road)... and I often need to shut it down if we need to drive or whatever. Not reall good on the hard drives to be using them when driving I do have the hard drives in a shock-mount bay that is part of the 4u rack-mount case, but I'm pretty conservative about letting hard drives take road vibration. I won't let my wife use our Thinkpad Laptop's on the road unless it is ON her lap... putting it on a table or other surface often "amplifies" the vibration when driving. Hence, it would be nice of the suspect worked correctly, as sometimes I want to get the machine up to check my email and quickly get it back down. Sometimes even at gas stations or quick food stops. The BIOS on our ThinkPad laptops sometimes gives us trouble (serial ports to modem won't work right 1 out of 5 suspends and requires a reboot). If I can get the system to suspend right, it will be nearly perfect!
Hope this answers your question (and then some).
EDIT: Just for kicks I did a suspend. Right during the middile of a DVD movie... came back up and movie continued, didn't have to do a thing. All my network connections restored too (including the wireless Orinoco card). So the Asus BIOS is already pretty good. One odd thing I noticed. While asleep, my CDRW and DVD drives had power. I could open tray and everything. The hard drives did shut down (I could hear them park and spin down)... I haven't played much with suspend on a desktop, maybe that is normal.