Lip prints are recognized as being a reliable means of identifying individuals, much in the same way that fingerprints are used. The methods used to match lip prints to an individual are very similar to those used to capture and compare fingerprints. The Federal Bureau of Investigation is among the law enforcement agencies that recognize lip prints as an accurate means of making identification, based on the knowledge that lip prints are just as unique as fingerprints.
More facts about lip prints:
Lip prints would only be available in specific types of crimes, since people usually do not touch anything to their lips while committing a crime.
This could prove someone drank from a glass at a crime scene, or even put some one at the crime scene at the time the crime was being perpetrated. However, I believe this would only serve as a circumstantial evidence, unless the item with that lip print served as a murder weapon.