Last year, it made me very nervous. I didn't get many interview offers early on, while others seemed to be getting tons. I didn't get my first interview scheduled until December and my last interview was in March. Your nervousness is understandable, but keep in mind that there is PLENTY of time left in the application cycle. In my opinion, SDNers are not a true representation of the applicant pool (I think we performed better than the average applicant on a whole) so it is no surprise that some people are getting invites as early as August and September. Yours will come, you just have to sit back and try to wait patiently. It takes time for an adcom to go through all of the applications. If I remember correctly, December was a really big interview month. I'd say November through February came and went with the most people posting different interviews. Maybe someone else could chime in an agree or disagree with my memory of last year's interview cycle.
I'd say don't worry about what you hear and see on SDN. Most of my interviews were in Feb and March. I even interviewed on the last day of interviews at UCSD. But I got in, and that is all that matters.