I haven't seen anything posted for 1.54 firmware so I thought I would mention it. I have two new YP-S3 devices purchased in November 2008 for Christmas presents so they didn't get opened till today. One is red YP-S3JARY/XAA w/ firmware 1.50c and one is white YP-S3JAWY/XAA w/ firmware 1.54. Both are labelled as MTP in Emodio software. I was bummed to find out that they would not load on my Windows 200O machine since that has most of my mp3 files. They have loaded inconsistently on my Windows XP laptop, but that machine has most of my audio files in AAC format.
They really should write the firmware so that you an switch between MTP and MSC from a menu on the device. Being able to readily switch files like a USB device between computers is a huge selling advantage over iPods and your missing out on a selling point.