According to Wikipedia, plastics with the identification code 2,4, and 5 "are believed not to leach chemicals in any significant amount." Plastic type 5, or polypropylene, is the most common material used in the type of backpacking cups at REI, for example, and it considered one of the safest plastics..
Lexan is a type 7 polycarbonate and according to wiki, "some type 7 plastics, such as polycarbonate plastic and epoxy resins, are made from BPA monomer. When such plastics are exposed to hot liquids, BPA leaches out 55 times faster than it does under normal conditions at up to 32 ng/hr."
You won't catch me drinking out of Lexan anytime soon, and I am suspicious of all plastics to be honest. Alzheimer's runs in my family and my sister refuses to drink out of aluminum containers because it has been reported that aluminum is a contributing factor for Alzheimer's, although some studies indicate this is not so. Not sure if that applies to anodized aluminum.
So I would say that titanium seems like a pretty safe material from a health point of view. I prefer to dance on this earth in good health as long as I can and so far I have been lucky.