Don't Index Wide Columns
If a table's columns are wide (i.e., the columns have a data type of char(25) or larger), indexes created on those columns might result in a large number of pages, thereby negating the benefit of using an index in the first place. Nonclustered indexes in SQL Server 2000 and 7.0 are structured differently from those in earlier releases. If you're not careful, you can create indexes that take more space on disk than the original data pages....