Clients may request up to 1,500 statuses via the page and count parameters for the search method. The response to a request exceeding this limit will be a status code of 200 and an empty result in the format requested. This artificial limit is in place to ensure the performance of the search system. We also restrict the size of the search index by placing a date limit on the updates we allow you to search. This limit is currently around a month but is dynamic and subject to shrink as the number of tweets per day continues to grow.
1. http://apiwiki.twitter.com/Things-Every-Developer-Should-Know#6Therearepaginationlimits