How effective are on-screen keyboards against software keyloggers?  

Windows 7 on-screen keyboard to be specific.  

They will definitely bypass hardware keyloggers but what about sophisticated software keyloggers? 

e.g. On a bank website, is it safer to use windows virtual keyboard or the soft keyboard provided on the webpage itself?

**Update**  

I am not saying that my system is infected.  

I am just asking this as a precautionary measure for the cases like when I have to use a PC in cyber cafe.