Lav technique
 

I have an omni lav. The manufacturer says to
face it downward, when placed on the lapel,
in order to limit the talent breathing onto
the mic. Manufacturer says because it is
an omni it will sound the same whether faced
up or down. Now, I haven't really looked
into this issue that closely, but it seems
to me that the recordings made with the
lav pointed down sound more "distant",
with less presence, as compared to the
ones made with the lav pointed up.
The manufacturer seems to imply that
this shouldn't be the case, but isn't it
true that if you were to talk to the back
of an omni lav that it wouldn't sound the
same?
A related question I have is that I came
across a person who seemed to be an
unusually heavy "nose breather" (for lack
of a better term) where he was constantly
breathing on the lav mic through his
nose. Any suggestions on lav techniques
when dealing with this situation?

It's true that it won't sound identical when speaking to the back of the mic, but as a general rule, the mic shouldn't be upside down anyway, but should be placed where the chin prevents the nose air from hitting it, unless you're in a very controlled situation ie newsroom. Folks tend to place lavs too low or too high in many situations.
My recommendation?
Sit down with a friend, have him/her breathe through their nose while you practice with the mic.
It's curious that a videographer would never consider going down to B&H, talking to a salesman, buy a camera, and 30 minutes later go shoot a commercial for national broadcast but that same videographer will go down to same store, talk to a salesman, and run right out with the new mic and expect miracles.

I'm not suggesting you may have done that, but I'd like to suggest that like a camera or anything else that requires skill, you sit down and practice with the mic while wearing headphones before shooting a single frame.

Sound is SO much more important than video, practice to get it right.

Douglas,
How close is too close? Is to the side better, or should it be centered? I've got a shoot coming up using lavs that are intended to be visible, so I can put them anywhere. Previously I used to hide them under the collar.

Make a fist, with the thumb extended. This is called a "fistmele" FWIW.
Put the bottom of the thumb beneath the lower lip of the subject. Where the bottom of the fist lies, is where you'll find the thick portion of the breastplate/sternum. This is the least resonant portion of the chest and is ideal for mic placement. However, it's not always ideal. But it provides a very nice starting point. When we recorded the 3 Tenors in Mexico City, I couldn't have the mic visible, so I bought 3 crappy Carter knock-off pens. These pens were perfect for holding lavs, and so the singers had nice pens in their pockets, no mics visible, slightly off to the side, and at appropriate height. Granted, it's rare you'll have vocals as loud as these guys, but it worked. And that's all that counts.
Experiment a little, but the target is that thick part of the sternum.

Thanks. Very helpful.

The 3 Tenors? I heard that Pavarotti used DPA
mikes at one point. What brand lavs did you use
on the Tenors, if you recall? And how does it
work with guys like them: do they bring their
own lavs, or do they just go with whatever
the sound guy puts on them?

In a live setting, unless it's broadcast, the Tenors don't use mics. Mics go against everything opera is about. They're pretty adamant about no mics showing up in a standard concert environ. DPA has Pavrotti in their literature, so I'm sure he endorses them. I'd like to try the DPA 4060, but after having had a little business correspondence with DPA, I'll likely never do biz with them.

I recorded the Tenors at 2 shows, plus one quarter-dress.
On one, I used ECM 88's, I think.
On another, I know I used Countryman B3's.
On the dress, I used AT 831's. (they wouldn't fit in the pen-heads)

I've recorded "Ireland's 3 Tenors", Mexico's 3 Tenors, and "3 Mo' Tenors" and in each situation, I think I've ended up using the Countryman in all of them, except for "3 Mo Tenors" because I used the AT 899 for those. I wish that mic had been available a couple years back.

Recorded into Echo Layla, then to Vegas, using additional mics in the house for both ambience and audience, plus a number of submixed mouse mics attached to the orch pit or other front mount to pick up applause, then fed to 4 subs in the 2nd Layla.