It never happened to someone to have those problems like "will the INCLUDE section satisfy my requirement to create 10,20,50... columns" It usually supports 3-digit or more number of columns.
It depends what types are the columns you plan to include and their definition. As many as you include as bigger in size the index becomes.
It also depends if your table already has many indexes, and the operations performed on the table. If it faces mostly read operations than it could be of value. If it faces 'quite' big amount of writes than it could withdraw a slowing down of update operations on the table. The table size is very important too. And of course some other factors should be considered too...
In general you'll be happy because naturally systems perform much more reads than writes. I'll suggest you to test. Create it, compare the maintenance impact, monitor your system, see the gain.
Igor Micev,SQL Server developer at Seavuswww.seavus.com