yes, and it could a combination of things:
ensure that message forwarding settings Redirect to Handheld is set to true, and Do not Redirect in Cradle is set to false. Message redirection should be enabled but if mail is going from the BB then it probably is. Ensure the redirection disabled icon is not showing for your users (a red dash on the user icon in Blackberry Manager). Check your pending messages for users - are messages building up on the server? Is data connection OK - can PIN messages get through? Get users to do 'reconcile now' and see if that forces messages to be delivered to the BB. Ensure there are no filters in place and that the setting on the handheld under filters is showing 'send email to handheld if no filters apply' - that's the big one for us that causes problems.
Groupwise client has a big impact on reconciliation - 6.5.6 is recommended, and I've just been told to get the rev 3 update before installing the next Service Pack.
If these tests don't work provide some more info (release level, number of users, settings etc) and we'll try again