I use the Verizon ExpressCard offering, the pre Rev A version, and I have no problems with it.
If I had it to do over again, I would get the Rev A card (not available when I purchased) and choose one with a USB connection. None of the cards are graceful, and they should be taken out of the conputer when not in use, and the USB card gives you many more options.
The only thing to consider is it is expensive. I have been thinking off and on about cancelling mine, but the times that I need it have been worth it.