A modern windows laptop with a SATA hard disk and a PCMCIA slot should deliver 2GB per minute or thereabouts. So, maybe 9 minutes to offload a 16GB card.
The adapter shouldn't slow anything down. Note, I said "shouldn't", I don't know if it actually does; hopefully someone will write in and tell us what kind of performance they get using such an adapter.
There are two adapters, one from Addonics and one from Duel. The Addonics one looks to be a lot more compact and is half the price, but doesn't yet work with Macs. For a Mac user the Duel is the only one.
The Duel has been field-tested and is a known quantity; I haven't heard any reports from anyone about the Addonics unit yet.