I think the big factors would be:
1. How internationals treat the Visa issue- if people dont care, then you would find a significant bump in the number of applicants
2. The fallout from the slightly flat-weak economy in the US
I am not sure how it was last year, but if you take a look at the b0week forums, the school specific threads are not very active. Either the number of users at b-week has dropped significantly (yay! GMATclub!) or the number of applicants (especially the domestics) have decreased.
The number of GMAT takers has increased YoY but I tend to believe that the number is stacked for the late part of last year AND an increase in the number of re-takes. I would say that almost 40% of test takes seem to be re-testers.
Also, I am not sure in other parts of the country, but in the midwest, the number of people looking into PT programs is also increasing. This would lend itself a little to the increase in the GMAT test takers as well.