Half an hour early? Fifteen minutes? Rush in right at 2 like Kramer?
I arrive at the building at 1:45 PM and head to the restroom. After freshening up, I arrive at the office at 1:50 PM.
Usually 10-15 minutes early. I despise being late.
Business appointment: no later than 1:45 or 1:50, if I can at all help it. I always build in extra time in case of traffic or other unforeseen delays.
Personal appointment (like a doctor’s appointment): probably no later than 1:55.
At least fifteen minutes early. The GF gets there after Kramer arrives. Just imagine how well this works between us. 
If I can manage it, 1:59. I usually can.
I usually try to be about 10-15 min early, more if I have have a long way to drive and traffic might be a factor.
Doctor’s appointment, I try to arrive 15 minutes early in case I have paperwork to fill out. (Today, traffic sucked - the doctor’s office is also located on the big shopping street in Chicago, Michigan Avenue, and everyone was out - so I only made it 5 minutes early.)
Business appointment, 5-10 minutes early. On the longer side if I know there’s a waiting room, closer to 5 minutes or less if there isn’t.
For a doctors appt, 10-15 min early.
For a professional appt, arrive early, but walk inside 5 mins before meeting time.
For a social appointment, etiquete states to arrive 1-10 minutes after the appointed time.
about 15 minutes early, as a matter of fact, only last week i had a doctors appointment, turns out someone else had cancelled theirs, so by being early i was in and out before my appointed time had arrived…! 
Ten minutes early. Always.
Depends a bit: When I had a 9:00 appointment for an interview, I happily showed up 10 minutes early. When they scheduled me for an 8:30 appointment the following week, I came exactly on time (because they started their day at 8:30 officially, and I didn’t want to come any before that).
Doctor - 5 minutes early if I can schedule it. My dentist is 2 blocks away, so not much traffic on the sidewalk. No reason to be earlier in most cases, since you won’t get in earlier. One exception - we go early to my wife’s retina specialist, since they schedule lots of people at the same time and being the first of the bunch can get you out much earlier.
Business - 15 minutes early in most cases, unless it is a meeting at a place I know well, in which case 10.
Appointment to get on a plane - an hour and a half often, just in case. I’ve never missed a flight, and I’ve come close only once or twice, but I hated it.
I used to be a stickler for being way early, but after thousands of times waiting for people who are late, I’ve changed.
Depends on the appointment, but I usually figure 5 minutes early is plenty. And for certain things, a minute early is plenty.
Like the doctor. I have NEVER seen a doctor early, and have been seen late countless times. So showing up on the dot is fine (unless it is a new doctor and I anticipate paperwork.)
I might be 10 minutes early for a job interview or a court call, but just about any other work appointment, prompt is plenty - no need to be early.
It varies wildly - if I care about being late, then I’m usually there very close to on time. But I have to actually care. Otherwise I’m often five to ten minutes late.
about 10-15 minutes early in the parking lot, and I hang out in my car about 5-10 more minutes.
Generally 10-15 minutes early.
Yeah, that’s about what I do. 15 minutes gives me a chance to tinkle and then get a feel for the environment I’m going into, so I can chill for the final 5.
Job interview: I will try to be early.
Dentist’s appointment: 2 pm
Doctor’s appointment: I’ll probably cancel it. I hate doctors. (Only professionally. I have some good friends who are doctors.)
Lunch with friend: Depending on the friend, anywhere from 2 to 2:30. (One of my friends is a known latenik. To be there early would be just a waste of my time. Being there late might waste a bit of her time, but she deserves it for having wasted so much of mine in the past.)
I always try to arrive exactly ten minutes early. Anything less is pushing your luck, and anything more is ostentatious.
A few weeks ago I had to interview some mook who came in for his job interview something like 35 minutes early. He was a horrible candidate, too. Couldn’t even implement FizzBuzz.