I have used the same 8 in 1 card reader for a couple of years and never gave any thought that readers varied much in download speed. But after hearing an interview with Lexar's Director of Marketing, Jeff Cable, I thought I'd give a UDMA reader a try.
If I'm shooting a wedding, I like to download and edit a selection of about 20 photos while the guests are having dinner. I then display them on my laptop as a Lightroom slideshow at the evening reception. The couple and the guests are happy and I leave a pile of cards on the table and generate more business.
There is limited time though for downloading, choosing the photos and editing them. It was taking around an hour with my old card reader, but the Lexar dual slot reader took under 15 minutes (including card swaps) to download almost 900 photos from both of my cameras 300x cards.