I was using S2U2 until I discovered PocketShield. There are many great features in this program.
For one, I use the light sensor to unlock. So when it is in a case, the phone will be locked. Once you pull it out into the light, it will automatically unlock. So it is there but it is very transparent. Once I pull it out of the case it is ready for use. No fiddling with a slide button or anything.....
It also has the slide to unlock features, as well as shaking or flipping the device to unlock...
Although the program is not free, they are running a half off special that ends today......
http://pocketshield.netserver01.com/default.htm