James,
Pretec has unveiled 64GB and 100GB, 233X Compact Flash cards, the highest capacity CF cards in the world. Now that should satisfy even the hungriest hi-rez camera and/or accommodate the new Hi Def video capabilities of the newer cameras.

I try to use the size card that will let me shoot a show all day with only one full download at night. That's always been a 4 GB card but I'm moving up to 8 GB with the 50D. I tend to agree with Jim Poor in that I'd rather only lose one day's work if the card craps out during a weekend shoot but I tend to monitor what's going on and I dump what I've shot onto my Epson P-2000 every 3 hrs or so. The idea of shooting an entire weekend of shows and never dumping the data scares the heck out of me.

But for most personal work and portrait sessions, the 4 GB cards are still ideal.

Jim