The only concern I have at this point is what is in the flavorings. Most of the USA eliquids companies are aware of the issues, I think.
http://www.e-cigarette-forum.com/forum/diy-e-liquid/127760-diy-warning-please-read.html
Personally, I wouldn't overdo the cinnamon but I really do think, after a lot of research, that ecigs are far safer and better for you than smoking analogs.
We don't necessarily know the long term effects on the lungs from the flavoring but we do know for a fact that smoking is a train wreck for your lungs and your circulatory system.
That warning was directed towards DIY people; you can find the ingredients of commercially sold eliquids in the CASAA pamphlet I linked earlier.
I avoid anything made with essential oils (cinnamon, citrus, clove) and eliquids containing diacetyl, but most producers are phasing diacetyl out.
I like clean, clear juices with as little additives as possible. I try to stay away from excessive flavoring, sweeteners, and coloring. But that's just me. Clean juices are also more user-friendly and won't gunk up your atomizer coils.