I use PocketShield.

It's free to try, you get nag screens from time to time if you keep the free version. I noticed their frequency to be extremely low at times (sometimes less than 1 in 100 unlocks). I actually bought it.

If you look over on their forums, the few people who run it are really fast on addressing issues... even updating the program for someone's issue within a few hours.

Overall, it's lightweight, can be unintrusive, and only needs minor tweaks from the developers to get it to a near perfect status.

It's definitely worth a shot.

Edit: Adding that the major downsides of S2U2 are that it's slow and causes a lot of problems, answering calls can be extremely late, etc... while nice, it's far from perfect and could stand to be cleaned up a lot.

Edit 2: Screenshot!