What would YOU do?

Just a small story that ended well, but I have to wonder if I did the right thing...
A long time ago, I was driving home with a friend late at night, when the person in front of me was weaving on the road. We both were pretty sure that he was drunk. So I used my cell phone and called the police. It was rather difficult, because by the time I got the story out as to who I was, why I was calling, and trying to describe where we were (while moving) we ended up crossing township lines, so they had to transfer me. Long story short, they eventually caught up to me and pulled the person over.

So, yesterday, I was driving home from work, and the same thing happened. I noticed a car that was weaving into the shoulder. Ok, once, no big deal, maybe he wasn't paying attention, and just drifted. We've all done that. But after the second time, my "spidey senses" kicked in and I thought, this aint right. So first thing I did, was back off the gas and let the guy get in front of me (rather than next to me, where he could have swerved into me!). Sure enough, as a space opened up next to him, he changed lanes and was now directly in front of me (though with extra space), next thing I know, he drifts over and ALMOST smashed into the concrete barrier separating the lanes of traffic! He jerked the car back at the last minute. So, I've got my hand on my cell phone, but now I'm having a hard time keeping up with him to follow, and other cars are now tailgating ME because I had given extra space between us.
So, I decided at the last minute that I would not call the police. I didn't have the number, (I've since added it to my speed dial - a good tip for everyone). He was pretty far ahead of me now so I wouldn't be able to follow safely and provide directions as to where we were. So I felt bad, but hoped that the near miss with the medium strip would be enough to get him to sober up.
Next thing I know, I seem him change lanes up ahead of me, and he gets off at the same exit that I was. him, now's my chance to catch up to him on the side streets. So I finally get behind him at the next light, but it turns out he's headed into MY parking lot of the apartment complex that I live at. So, it doens't make sense to call the police now, because by the time they get there he might be parked and out of his car. So I follow him, to make sure he's parking and not continuing to drive. Finally, he ends up parked and as I drive past, he's getting out of the car.
So here was my dilemma now... Do I say something to this guy? Do I risk a confrontation with a drunk to let him know what he did was wrong and endangered not only his life but others?!
I decided in that split second moment, that if he's drunk, I wouldn't be able to rationalize with him, so I passed him by.
But now it's still nagging at me, as to wether I did the right thing or not. I think I did, but...
So what would you have done? confront? or make sure he was off the road and continue on.