My personal experience with this exact problem was to uninstall the onscreen display and hotkey software that was pushed via ThinkVantage System Update. I then reinstalled the original driver package that was located in the C:\SWTOOLS\DRIVERS\HOTKEY folder. It appears as though later versions do not work well with SP3. This restored all the hotkey functions as well as the blue ThinkVantage button and the onscreen display.
There are several common problems emerging with Access Connections, wireless drivers, and the hotkey functions that are clearly the result of insufficient testing of SP3. As to who is responsible for the testing, Microsoft or Lenovo, you can have your own opinions. I for one, think Lenovo should have been on top of this.
I did exactely what you suggested (important precision : to uninstall you have first to execute the program you spoke about) and now I have everything working with the old driver (May 2006) :
Blue key : works again Fn F2 : is working Fn F3 : is working Fn F4 : is working Fn F5 : is working Fn F7 : is working Fn F8 : is working Fn F9 : is working
And I took one hour with a top-level Lenovo manager to show him the problems but thank to your help I already got the solution when he came... He suggested that maybe my antivirus or another program could block the new hotkey driver
But it still doesn't work if I do a system Update of hotkey. So I won't do it...