First I must apologize for my ranting. But let me blow of some steam, please. I wont be an ignorant fool and claim it's all the cameras fault, because it's most likely mine (fastest (class) camera in the world and an L w/USM lens? No way).
OK...first things first... if you were a chick and you said you sucked with a 1D.. I would ask if you were available 
(ok, that was low..
)
Now on to the real advice.. whenever you transition to a new camera and system it does take some practice. Also be aware that some days are just bad days. Some days even IS doesn't help me because I am so tired and shaky. You might really want to just go there and take it easy because the 1D can be a trying beast to carry especially with full getup.
I really don't like the 1D's LCD, I don't even chimp.. that bad, for someone who does so often and necessarily on the 5D.
CF card problem: Carry a spare card and be prepared to change out and format immediately. Just the way you carry a spare battery. Countless times I have showed up on location and discovered the card is still in the card reader.. countless times the 1GB or 2GB spare (or even the microdrive!!) in my bag has at least enabled me to start shooting and stop looking like King Moron (unfortunately a hat I wear fairly often too)
The other reason is that the 420EX AF Assist does not cover all 1D points. I believe the big 5x0 series flashes do, but not the 4-series. Read manual again to just be sure.
1D AF has been acknowledged by the guru himself (Chuck Westfall) to be slightly inferior in lower light UNLESS there is AF assist light. He specifically recommended adding a flash or ST-E2 to do the job.
There is a delay while the AF system tries, misses, orders the Speedlite to fire the red AF Assist beam, then tries again. It may be 2X the normal AF time, I am not sure. This delay has always been noticeable on every one of my Canon DSLRs. I think Chuck mentioned something about AF speed being affected by this too.
It is safe to use all AF points even at f/4, however, because of the limited flash coverage, I would go for the backup - set center-point ONLY and go for that. I use center only when I need maximum reliability, and no, FLR does not seem to trip me up even though I use it lots at events.
IMO, AFPS and Area AF shine in BRIGHT light, which is the domain of my 1D. I know it's your primary camera so you'll have to find a way to make it work and with a little bit of help it can be done.
Image stabilization on short zooms is REALLY useful when you want to drag the shutter like this. 24-105 FTW!! 
Clubs with low light, moving people, and everything - are extremely challenging places to shoot. I feel for you as well..I'd buy you one if I was nearby. I think it' s just a bad day. Put the camera away, or take it out just to demo it, where there's no pressure. And order a few more drinks! You sound like you need them 


