I did my own taxes since I started working at 16. I have also done other peoples taxes for them in the past.
Several years ago I started using an accountant because they got more complicated and I just did not have the time to do it and keep up to date on all the changes.
It is a much better feeling and use of my time to just have someone do it. I keep good records and just bring everything in and spend an hour or two.
The peace of mind is great to have a professional behind it as well.
The market reflects this in that organizations are now offering free returns for those who have more simple financial returns.
To answer your original question, I think it is about the same amount of people filing their own because in general there are not that many changes in the tax law this year to last.