After a little more research, I've found out that all ExpressCard 34 readers are not created equal. The Delkin ExpressCard 34 Compact Flash adapter sells for $26.50 at B&H and transfers files at up to 40 MB per second, which is roughly the same speed as a SanDisk firewire 800 reader that costs around $60. The Sonnet Pro Dual Compact Flash Adapter ExpressCard/34 sells for $97.95 at B&H and transfers files at up to 133 MB per second. So the Sonnet adapter is 3 times faster, and over 3 times more expensive, but can transfer data from 2 compact flash cards at once. I believe Michael and Jeff used the Delkin adapter in the Lightroom 2 tutorial, but I'm not 100% sure about that. I think the Sonnet adapter was released after the Lightroom video was produced. Lloyd Chambers recommends the Sonnet adapter for those who choose to use an ExpressCard adapter.
The fastest transfer speeds can only be utilized with the fastest UDMA cards. I don't see any advantage to using the fastest, most expensive card reader with slower compact flash cards. Still, this raises an interesting point. If fastest possible data transfer from camera to computer is needed, it makes sense to use the fastest compact flash card and the fastest card reader, even if your camera cannot take advantage of the fastest cards, for example a Canon 5D (not MKII).
Lloyd Chambers also points out that the ExpressCard 34 slot on a MacBook Pro cannot be used for anything else while the card reader is mounted. This would present a problem to those who might want to transfer files to an external hard drive via an eSATA connection, which also utilizes the ExpressCard 34 slot.
This may all seem like much ado about nothing. Most of the time, I just take a break when transferring files from 4 GB or larger cards. One has to ask how much it's worth to achieve the fastest transfer speeds if a client is looking over your shoulder immediately after the excitement of a shoot. For me, it's worth an extra seventy bucks or so.
