Maybe others know about this but I never had the need before since my Xoom has a microSD card reader.
Anyway on a recent OS trip I wanted to watch content on my Galaxy Nexus on the plane. But it only has 16GB and I had almost 24GB of files I wanted to watch (in .ts format). The phone can play them fine, just can't store them.
I then discovered the above app from the Play Store which when combined with a microUSB cable to USB female, allows you go read content of (FAT32) formatted USB sticks and drives. The software is US$3.99 and the cable cost me US$0.99(!) including shipping .
Anyway attaching the cable and then USB drive allowed me to play all the content off the USB drive so I really didn't need more storage on the phone.
That means I am now more inclined to purchase a Nexus 10 and not be worried about internal storage limitations.