I think I agree with Pauline, 1000 a month should be quite ample, unless people are breaking the terms and conditions and doing thousands of lookups for other people and making money out of it!!!! 
Kerry
It all depends on how you do your research....
When it 'costs' 30 to view an image and 10 for the record, it is actually quite easy to reach 1000 when you are researching a large family and like to follow your ancestors and their siblings (often several in those times) and offspring into 1911.
And if you like to arrange your research by census households, so you can see who is living where and who they are living with and who they are living next to.
And if you also like to see the actual page and not just a transcription, esp as we can now see the forms they filled in themselves.
And if you are trawling for a particular person and have the hunch that they are hidden in a street ....and then you don't find them, so have to look elsewhere.
I am obviously going to have to find a cheaper way of trawling the streets on site, but just wanted to point out that it can be very easy to reach 1000 through personal, I agree enthusiastic, research without having to defend against the accusation of abusing the conditions, making lots of money and doing 'thousands' of searches for others.
1000 credits = e.g. viewing 30 images and 10 households