dpreview.com is shutting down their user articles section. This is something I wrote September 29, 2011
A fair number of people exhale on their lens surface. Zeiss or some german brand says it's ok. Nikon in one quote says that the exhalation has acid (actually, your saliva is alkali but you may have acid from food or stomach) and is not good for their nano coatings. I used to use Kodak Lens Cleaner, now use some pocket spray from a UK optical company but not directly on the lens, on the cloth. I don't mind exhaling in an emergency when I don't have these liquids.
Mostly I use air blower or soft brush end of a Lenspen first. If there is a smudge, I use the Lenspen - it has a powder coated felt that aggregates the smudge without the need for fluid, then brush off.