1000
That's no more than an educated estimate of the point where fragmentation will start to have a noticeable effect on range scans from disk. It is not the point where an index seek is cheaper than a table scan (which could be anything from a few pages to never, depending on covering state of index and count of rows returned)
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability