I use a Y cable that a mini USB plug and a charger tip at one end and male USB plug on the other end. This works nicely for chargin on my Desktop. However, one day I had both USB and power plugged into my IHP 120. When I plugged the other end into my laptop, it just switched off. I haven't really tried to reproduce this since, because I'm not too keen on frying the USB port in my laptop, or even the laptop itself.
So I would rather not have this mod inside my Iriver... with the cable I can either 'just charge' or 'just plug USB' if I'm not sure the USB port can handle the current that is drawn. Additionnally, I wouldn't want to be charging each time I plug in... I like to let my batteries come 'close to empty' before charging them. I still believe this enhances their overall lifetime a bit...
Hope this helps you decide wether you want to try this mod
Have a nice day,