I've got the android lock XT and that's plenty of security for me. It's a simple swipe so I can open it quickly when I need to, but it's confusing enough that friends can't break into my iPhone. I have a PIN for bite SMS just because I hate people reading my texts, and that hardly gets in my way because I can start testing from anywhere without needing to do the code. Luckily no one knows that feature...
I use the PIN. Thought I was gonna switch to Password when I first heard about the availability, but I thought it'd be too annoying. I change my Pin every couple of months for added security.
