When designing the interaction for websites and using javascript it is always important to make sure it degrades gracefully. That said, how many people cannot see content because they lack javascript. When working with ajax calls, you create pages people can be taken to when they don't have js. The practice is to default to those pages, and I'm not talking about such heresy as not doing that anymore. However with some projects there is too much time involved in having this perform as well as can be. So before I plan to do a vary simple solution for non-ajaxians, I'd like to know some statistics of how many people I'm "leaving behind".
I haven't been able to find any concrete numbers.