Apparently, there is a new firmware 1.71. I don't know the exact changes and have not installed the fw myself yet.
Some Information:
http://www.gennard.net/blog/2010/04/...firmware-1-71/
Korean site with what seems to be release notes (I do not read korean):
http://zone.iriver.co.kr/service/cs_...Idx=1&idx=1217
Other place to download, this is where I tend to look for updates. No release notes there (yet?):
http://www.iriver.com/index.asp?code=0402
Edit:
I have installed the firmware. The overall speed and responsiveness seem to have improved a lot.