Product Version: NetBeans IDE 6.0.1 dev (Build 200801100000)
Java: 1.6.0_05-ea; Java HotSpot(TM) Client VM 1.6.0_05-ea-b06
System: Linux version 2.6.5-1.358 running on i386; UTF-8; en_US (nb)

When control is pressed and mouse cursor is hovering over some element, the popup informing about the target is opened.
For generic type this popup is empty.

Example: press control and move cursor over T in method declaration in following class:

public abstract class Response<T> {    
    T resp;    
    public void getResponse(T resp) {
        this.resp = resp;
    }
}