Performance impact of having gaps in Identity Column in SQL Server 2005
I don't see how gaps in your identity values could have A N Y negative impact on your performance.

After all - the values are still all 4-byte integer, they're still as optimal for JOINs as anything can be ..... and even if you have gaps, the IDENTITY values are ever-increasing....

Of course, if you physically deleted rows from your clustered index, then there will be "holes" in your pages (the "Swiss Cheese" problem :-) ) - but those would be fixed by a nightly database maintenance that you certainly do have in place, don't you??

And even if you do occasionally delete a row from your table, the impact on your index fragmentation will be marginal.