Hmmm, I'm trying to do the math, and it seems like you get 1.5 kiloyears of cacheing at 1 meg/minute before your compact flash card has had 100k writes, assuming a 0% cache hit rate. if that number is correct, I'd say definitely cache to the card, unless the writing out take a non-trivial amount of processing power.

Of course, with the price of compact flash falling, the compact flash empeg is going to be more prevalent than the hard drive empeg soon enough.

Matthew