Believe it or not there is no law against following someone one single night, even if it is to their home, as long as you do not make threats or otherwise assault the individual. It might be irritating but it isn't illegal.
I once followed some guy on the freeway from the freeway at bangerter all the way to clearfield. He was driving like a douche, so I definitely noticed him, and once or twice even pulled in front of him after he passed me just because I could and it fit in the flow of traffic, then he would find a tiny niche and get his giant 4x4 roaring to get around me, and others, again, obviously pissed. I followed him off the same exit into clearfield, then believe it or not, directly behind him into my sister's neighborhood. He pulled over a few houses before my sister's house, at his own house presumably, and I had slowed down as I was approaching her house, so I suppose it looked like I was slowing down in front of his house, and he got out and ran around his truck gesturing and yelling at me. I debated driving around the block first, but decided that was crap to have to do that and pulled over in front of my sister's house like 3 houses down and he followed me, swearing and waving his arms. I was afraid to get out so I rolled down the window a crack and he "asked" me what the **** I was doing following him all the way from salt lake city and did I want to get my *** kicked. I explained quietly that my sister lives right there and I was just getting off work and was coming here for a family dinner, that I wasn't following him and that it was just coincidence. He called me a liar and threatened me again, so I called my sister and she came out and he got red-faced, still pissed, and stormed off.
What might have happened if I had jumped out of my car and gotten in the guy's face? What if he had just gone inside and ignored the whole thing?
If Martin had just gone home, had not doubled-back, and gone inside he would presumably be alive today, even if Zimmerman had followed him to his very doorstep. Even if he had done so swearing at him, calling him the N word and threatening to kill his family, if the kid had just gone home he would likely still be alive today.
But like GF said, there is an entire thread devoted to this, with some good commentary on both sides. Anyone interested can go read it all there.