I bought one for my neice. Small screen (obviously) but the interface is pretty much the same as on the 405 & 605 (actually it's got a lot more colour customisation options than my 605). Videos need to be encoded to WMV9 at a resolution of 160 x 128 but they look ok on the screen. I think Windows Media Player 10 or 11 will correctly recode these automatically, but I've yet to try it. As with all the current crop of players the sound is pretty good but would benefit from a decent pair of phones. All of the players sounded great using my Sennheiser CX300 canal-type phones, which I can thoroughly recommend for listening in a noisy environment like a plane.
Here's a tip for batch converting a folder of photos so that they fit and look ok on the 105. I used IrfanView's batch converter.
First open IrfanView and press "B" (or choose the batch conversion option from the file menu).
Then set your output folder to wherever you want to save your files - I'd recommend using the same one all of the time and then simply move all of the files to the 105 after conversion, leaving the folder empty for the next batch, as IrfanView will remember the folder you've specified.
Decide whether you want to keep the same file names or not - you can define some sort of naming pattern to use (e.g. Xmas2007###) to avoid duplicating file names which may already be on your 105.
Set the output file type as jpeg and click on the options button to make sure you've got it set to best quality.
Click on "Set Advanced Options" and then use the settings exactly as shown below
All in all I think the 105 is a great little player at a great price - I might end up buying one for myself yet, and they make great stocking fillers.