For those of you using HMC 3.5 (or plan on using it), there is a change in the Plans system when creating a new plan for Outlook client access. It appears that the sample XML request provided with the solution is also out of date.
Enable Outlook Client for a Plan: HMC 3.0
<feature>
<featureName>OutlookClient</featureName>
<featureDescription>Full Outlook Client Access enabled</featureDescription>
</feature>
Enable Outlook Client for a Plan: HMC 3.5 (and the Feature Pack)
<feature>
<featureName>MAPI</featureName>
<featureDescription>Full Outlook Client Access enabled</featureDescription>
<featureValue>0</featureValue>
</feature>
The main change here is the "featureName" is different. To enable a feature, the "featureValue" must be marked as "0". To disable the feature, you must set the featureValue as "1". If nothing is defined for that feature in the plan, then the Exchange Server defaults (assigned at the Storage Group level) is applied.