In general, the workflow for Cases is awkward, inefficient, or actually misleading.
1.) Currently, it appears that an activity must be saved before the option is even presented to associate with a case. When creating a new activity, the Cases selector doesn't even appear. So the workflow is: Create a Case, Create an Activity, Edit the Activity you Just created, assign it to a case. Yuck. I count NINE page loads from CiviCRM home to just start a case with one activity. (Not counting extra refresh caused by #4, below).
2.) When viewing a case with no activities, a message is displayed that an activity can be added using the 'activities tab.' However, there are no tabs on this page. I propose that the primary view screen for Activities & Cases should be the Cases Tab, which a tree-like display of all 'Active' activities under it's given case (or under an 'Unassociated' section for activities not associated with a case.) This page should include links for adding new activities associated with each case. Normally a user shouldn't need to view a 'Case' on a standalone page, but when they do, that page should have the tabs for the Contact through which they navigated to the case, or their own tabs if they arrived at the case page some other way.
3.) Should there be a new 'Your Cases' section on the Dashboard?
4.) When adding an activity, the refresh caused by associating a contact (is this necessary?) also triggers validation, which means I get a big ugly Warning because I haven't yet reached the required Subject field. Validations should not be triggered until the user actually clicks 'Save.'
5.) It'd be nice to be able to add Custom Field groups for Cases, as can be done currently with Activities.
6.) It'd be AMAZING if that E-mail-to-Activity script that was floating around could be incorporated as an Email-to-Case tool...
I'm really looking forward to adding Cases into my projects, and it has come a long way, but right now, it's major shortcomings (#1 & 2 above) are so annoying that I can't recommend it as it is.