I applied on October 3rd, 2013. Payment was processed the next day.
I obsessively checked my application every single day, at least once a day. After two weeks, I called to ask how long it usually takes, and they said it could be up to three months. Last week, which was the 5th week, I called numbers for both the Canadians and the Americans. The canadians told me that they approved my background check, and that I had to wait for the Americans to process it and approve it. They said that the americans would take about another 6 weeks or so. When I called the Americans, they told me that minimum, I would find out by December 3rd, which was the 8 week mark. but it could take up to 12 weeks. So I was surprised to see an email that I was approved this morning. I scheduled an interview at the Niagara Falls border crossing for January 8. It was the best option that didnt conflict with school.
I was in Toronto this past weekend, and when I went to Pearson International Airport for my return flight home, I asked the US Customs Officer at the preclearance if he knew what it was like for the interview at the airport. He said that they are backed up with applications for interviews at Pearson, and the best thing to do would be to get an interview at a border crossing. When I checked the schedule online, the next available apointment was in the last week of February or the middle of March. The airport in Montreal was booked up till February also.
The Port Champlain border crossing has a few openings in the last week of november, and is pretty open during the month of december. this is the border crossing on the way towards Montreal, and is about an hour north of Plattsburgh.
The buffalo border crossing is also booked up, but they do have some available apointments scattered over the course of a few weeks.
It really depends on how far you are willing to travel and when you can go for an apointment.
For those of you on the West Coast, beware, because I saw that the airport in vancouver was backed up until May, I believe. And I think the nearby land border crossing was backed up a few months as well.

To get conditional approval, it took me 5 weeks and 6 days. I am an american citizen with a zero criminal record. and zero traffic violations. not even a parking ticket. and i have not traveled to high risk countries such as libya or Somalia, which may cause the application process to go on for longer than others.

If you plan to make an apointment at a border crossing, you should know that they do not scan your iris at those interviews. you would have to visit one of the canadian pre-clearance airports to have your iris scanned, which you can use when going through customs while arriving in canada from abroad. to have your iris scanned, i do not believe you need an appointment. I think you can just show up.

after the interview, I believe it takes about a week to receive the NEXUS card in the mail.