Well it has been over a month since anyone last saw anything new on the PC version. However it appears the Italian magazine "The Game Machine" has had a sneak peak and revealed some new details :-

• The replay editor will record the last 30 seconds of gameplay. Once the video has been saved you can use inbuilt software in GTA 4 to add special effects and change camera angles. You will also be able to add audio tracks from the official soundtrack of the game (no word on whether you can use your own MP3's). Once your video is done it can then be published on Rockstars Social Club site so others can watch it.
• The GPS and map have been beefed up, thanks to the mouse it is now just point and click. However Rockstar have added the ability for you to mark locations, make notes and add images. That should make hunting those pesky pigeons a bit easier.
The other important bit of information is that Rockstar have managed to improve the game streaming, thanks to the power of the cpu in modern PC's. This means less of the "same car syndrome" in which you would see lots of the same car you are driving. The magazine is also claiming that there will be more pedestrians and vehicles visible in the PC version

Link: gta-series - New details