Not a bad idea as a back up to faulty cards, but the transfer is very slow. I purchased the adapter for the same reason, I have 60 gig of available space on my Ipod...why not put it to use.
However, at 500k per sec, there are better options for me. If you are planning to transfer gigs of data, better off buying more/larger CF or other storage media. One advantage is that you can pass your Ipod aroud for others to view while you shoot additional shots