It has been a long time since I have worked with MS Access and am not sure if I am doing this right.
I have a Report bound to a query of single list of user names. T
To get the full benefit of subreports they should be bound to a recordsource (table or query) and use the Link Master Fields and Link Child Fields properties of the Subform/Subreport control to "sync" the subreport data with the parent record.
Say you have a [Users] table
userID
------
Gord
Tim
and a [UserTraffic] table
userID trafficDate downloadMB
------ ----------- ----------
Gord 2013-04-26 366
Gord 2013-04-25 442
Tim 2013-04-26 890
Tim 2013-04-25 212
Your main report [UserReport] is bound to [Users] and contains a subreport control based on the report [UserTraffic_subreport]

When you use that report in your Subform/Subreport control on your main form...

...be sure to set the Link Master Fields and Link Child Fields properties...

...so your report will come out like this:

Note that this example required no VBA code at all.
The same principles apply when adding a chart to a report. The following report displays user traffic by date, so the Record Source for the main report is
SELECT DISTINCT trafficDate FROM UserTraffic ORDER BY trafficDate;
The report uses a Chart control instead of the Subform/Subreport control...

...and the properties of the Chart control are...

The resulting report looks like this
