It will go up as soon as the test of 21181*2^2115523+1 finishes.
The number of digits in k*2^n is approximately log(k)+n*log(2) or in our cases 0.3*n+5 (or 4 for the smaller k's).
Judging from the graphs of the remaining tests, the second smallest number being tested at the moment is 24737*2^2325702+1 which is a number with a little over 700000 digits.
As others pointed out when Louie announced the addition of this number to the stats page, it's held back by the slowest machines, and it would be a lot more interesting to known the number of digits in the largest number tested, which is well beyond 950000 at the moment.
Edit: The largest completed test is 22699*2^3293614+1, a number with 991481 digits. (And some spelling fixed too)
.Henrik