I am using a SanDisk UltraII 8 GB HDSC card, and have experienced no problems. I think the manual says 4GB, because when it was written, that was the max size available.
I took a 4gb card along too, just in case.
I really like this setup. I dove with a Nikinos V for many years, but focus was my main problem. I am using the rechargable battery and did experience battery failure on one dive, but thatwas my fault. Inexperience. One thing to save posser is to set the screen on preference so that it goes dark after 1 min of inactivity. I had my set to 5 min. and it really eats through the battery time!
The diving on this trip was a little problematic, due to rough water and over-loaded dive boats. I was having trouble reading the screen in the water, partly due to a mask fogging issue and partly due to the screen getting dark. (Also a little age-related nearsightedness)
I shot entirely in manual mode and was consistently underexposed. Fortunately the RAW format is very forgiving. I attribute all this to my inexperience with the rig and expect to do much better. I am very leased with the camera and the setup.
I am going to be on the Komodo Aggressor in October and hope to perfect my technique.
Here are a few more photos with the wide angle lens

