I have the same problem. The unlock slide becomes sluggish only when the phone app is running (perhaps along with some others services) and refuse to slide all the way to the target green dot resulting in missed calls. The same problem continues during the call as well after screen goes blank after some time into the call and I have to unlock the phone before I can use the touchpad during the call. The sluggishness goes away when phone app is not running.
A solution I use for this problem is a free app called ScreenMode Widget I found at the market. It has three options:
1: Sleep Auto
2: Awake Stay
3: Screen Stay
To change between them just click on the widget icon and it will cycle through the three. Option 1 keeps phone's default operation. Option 2 turns off the lock feature. The screen will go blank after set time, or when you hit the top power button. When you hit the power button again, screen returns to where you were without unlock. Option 3 keeps the screen on until you turn it off with the power button. I keep it on Option 2. The only thing I need to be careful with is to make sure I don't trigger the phone with volume locker or the camera button as I put the phone back in my belt holster (otherwise the screen will be on for the next two minutes wasting battery without my knowing about it).
I sure hope someone will fix this one of the two most annoying problems (the unlock slide and lack of bluetooth dialing capability) with Droid.