I really like this app. I was skeptical at first, so I decided to run a simple test. My goal was to drink more water. So I setup a "Drink Water" message in Subliminal. The first day I think I was too focused on detecting whether my behavior changed to actually conduct a decent test. However, after a full week running Subliminal, I've noticed I have been drinking more water. I have gone from drinking less than 500mL during the day to consistently drinking more than double that amount. I'm going to keep the message running for the next 3 weeks to see if it'll help me establish the habit of drinking more water.
I recommend giving the app a try. Setup is quick and the interface is really simple, which is nice. IMO, it's worth it to see if at least one of your New Year's resolutions will stick :)