I don't think the law is literally enforceable -- as in, a cop is going to say, as he's driving down the road, "Hmmm, that guy is only two feet away from that biker. I'm going to pull him over and give him a ticket." At best, what it might do is, if you get hit, there's now something specific that can be thrown at the driver (he had to have violated your three feet.)
I haven't commuted this week (lots of oddities about my work schedule at the moment), so I can't say anything about the drivers in my area. I've been wondering, though . . .
I had an "encounter" about a month ago as I was riding home from work. I had turned left onto WB&A Road from Donaldson. WB&A at that point is narrow, two lanes, and with zero shoulder. At the first stop sign, which is maybe 200 yards (if that?) from the light, I turn right, and into the tiny streets of my neighborhood. I have learned that drivers on this stretch will often squeeze uncomfortably close to me in passing so that they don't have to go too far over the double yellow line. Consequently, I ride a little further over to the left that I might otherwise, making it clear that if they want to pass me, they're going to have to commit to going almost entirely into the other lane. And they do -- I rarely get "squeezed" there anymore.
(I've never understood that mentality, by the way . . . as soon as you stick your nose across that double yellow, you're risking a collision. So whether you put just 1/3 of your car, or your whole car, across the line, it doesn't much matter in the end.)
Anyway. I hear (and see in my mirror) a pickup truck approaching. I do some calculating, and I realize he's going to catch me shortly before I get to the stop sign, and there's oncoming traffic, so he's going to have to wait a minute. (Not literally a WHOLE minute, of course!) He's staying back, though, no trouble there. But when he pulls over to pass me, he leans over and yells through his open passenger window "Why didn't you move over out of the way?!!" For some reason, it ticked me off. I was only seconds behind him to the stop sign, and when I saw him turn into my neighborhood, on impulse I followed him.
I must have been out of my mind.

I am normally the least confontational of people. But I followed him to his house, where he stopped (but didn't get out of the truck) to get mail out of his box. I was standing alongside the truck, a little forward of his passenger window, patiently waiting. He knew I was there, but refused to look at me. (Yah, I'm *so* intimidating, right???

) When he wouldn't acknowledge my presence, I actually got off my bike and walked around to his side of the truck. (I still can't believe I did this!)
I was very nice and polite. "Excuse me, sir, I live in this neighborhood, and I don't like having any bad situations with my neighbors, so I just want you to know, I really wasn't just trying to annoy you back there on the road." And he immediately launched into a tirade: "Why wouldn't you move?? I've never seen anyone ride like that, I see cyclists going up to the BWI trail all the time, they don't do that!" I said "Well, the road isn't wide enough right there for both of us to fit, so . . . " and he interrupted "Well, you shouldn't be on it then!" And I got pissed -- still not yelling, but rather firmly "I have as much right under Maryland law to that road as a car does." And he interrupted with the classic "Oh, you have tags on that thing?" "That doesn't matter." "Yeah, right."
And then he started in again, "I ride a bike all the time" (which I seriously doubted) "up to the trail, and I never see anybody doing that! That's where you're going, right, to the trail?" (That last delivered in a really snotty tone.) I almost lost it then, and fired right back (very stiff, and slowly, but still no yelling

) "No . . . I . . .am . . . not. I LIVE here. I'm on my way home FROM WORK." (pointing to my garment-bag pannier.)
He looked just minorly sheepish then, I gave up and pulled away, he went down his driveway. I haven't seen him again, but I've been wondering what he thinks of the new law, and hoping he didn't read that stupid Baltimore Sun summary.
After he left, and I rode off, I realized (I don't normally ride down that street) that his is that weird, compound-like place that's surrounded by fencing and trees and warning signs. It's a big property, and on the part that faces WB&A Road (north of that stop sign) there's a HUGE, permanent (I'm talkin' like mounted on 4x8's

) elaborately painted "Sarah Palin 2012" sign. It's been there for at least the nearly two years that I've lived there.
Just sayin'.

Actually, now that I think of it, I guess I don't have to worry about him having read that Sun article; a true devotee of Ms. Palin wouldn't have any truck with that Communist rag, anyway.