Big CF cards are quite expensive and I played around with some small ones before purchasing a 32GB card. With the card being >90% full I had heavy problems with the system hanging and ended up planning to buy a SanDisk Extreme III.
In contrary to most SSD as nowadays CF cards commonly do not support theTRIM command which allows the operating system to tell the card when blockson the disk get free. The internal storage software of the CF card can nowreuse those blocks for new data. To my knowledge there is no solution for that.
I don't have a camera that uses both types to do a direct comparison, but my impression is that the CF cards could be a bit more rugged and therefore more reliable? But then again the SD cards are certainly cheaper, especially in higher capacity. I think the same rule applies, that if you buy a good quality example of either type, SanDisk, Lexar for example, they are pretty reliable.