Ephi Blanshey:
However, if I meditate using the noting technique of labeling everything that arises in my consciousness, does that also not lead to ultimate concentration on the objects that pass through my awareness? In other words, in a way, I'm concentrating my awareness, not a single object. I'm interested in what others have to say about this.
Yeah. That's basically it. Concentration factors into choiceless noting in the sense that you can be (1) ardently and persistently noting the sensations, (2) noting in an absent-minded manner, or (3) not noting at all and falling off into fantasy. (1) is the most concentrated, (3) the least, and (2) in the middle. You'll find that your noting will fall closer to (1) as you approach the A&P and the 11th ñana, but in other spots there will be a greater tendency toward (2) and (3).
Concentrating on a single point is difficult, as I notice all sorts of distractions often, whether in the world around me, or very subtle bubbling of thoughts, or other mental movements.
The main obstacle to what you're calling "concentration" here is the relative calmness (or lack thereof) of the mind. It's not so much the willing of the mind on to a single object. It's how much the mind is wound up. If you want to get good at concentration (samadhi), it's best to work on calming the mind (samatha).
That being said, you don't need a mountain of samadhi to get stream-entry (I assume that's what you're interested in). To get stream-entry, you have to get the mind really good at letting go of things. This is probably why noting is so useful for stream-entry. When you note a sensation, you put distance between your awareness and the object. It's like dropping it like a hot stone. If you do this in a comprehensive-enough way - applying it rigorously not just to the sensations of the breath or the things you notice in the body, but also to space, time, desire, attention, memory, and finally consciousness and awareness itself - you'll get the blip. Looked at that way, getting stream-entry isn't that hard. You just have to be persistent.
I've found that it's the territory above 2nd path that really requires the most samadhi and hence samatha. You're trying to get at much subtler stuff, so the mind has to get still. You can imagine the mind here vibrating and moving around so much, that it can't maneuver itself into small spaces. It has to calm down, become much more still, and then the subtler phenomena become conspicuous. This is seen clearly when you try to access the arupa jhanas. These states are subtle, and it takes a pretty still mind to be able to access them. If all you're doing is noting - no matter how persistently and continuously you can do that - you just won't be able to access those subtler states.
All that being said, bringing more samatha to the practice never hurts (so long as you're noting diligently). It makes going over the rough spots of the path (particularly 3rd ñana and ñanas 6-10) a lot nicer! To that end, there's a lot to be said for mixing samatha and insight and not separating them into two, distinct practices the way the Vissudhimagga recommends. But if I had to recommend just one practice to get you stream-entry, I'd say: just get really, really good at noting (which basically just means keep practicing it whenever you get a chance), and that should do it.
Just one yogi's two cents...