I modified the SProc to roll up reports by ReportName and count(*) to see which reports are the heavy hitters and which ones never get run.
Here's the modified SProc:
SET ANSI_NULLS ON
SET QUOTED_IDENTIFIER ON
CREATE proc [dbo].[report_usage_grouped_by_report] @report varchar (75), @user varchar (15)
select -- report path and name
from reportserver.dbo.ExecutionLog E
join reportserver.dbo.catalog C on E.reportid = C.itemid
where (C.name = @report or @report = '
and (right(E.username,3) = @user or @user = '
group by C.path
order by 2 desc
--execute report_usage '
--to feed your report parameter @report
select name from reportserver.dbo.catalog where type = 2
--to feed your report parameter @user
select distinct username from reportserver.dbo.ExecutionLog