Exchange 2010 Email Archiving

So are policies and administration of the archives done within Outlook by the user or can it be controlled in Exchange?

You assign policies to the users and outlook users can archive items based on these policies. On my test rig I have two policies,

1st is 1 year delete Personal
2nd 1 year move to archive

I can tag my emails with either of these policies so items I wish to retain are archived and personal items I'm not too bothered about are deleted after 1 year. You have plenty of flexibility on policies and they can be configured as per admin requirements.

Exchange has a litigation hold where users are not permitted to delete anything, personal archives have retention hold where no items are deleted from a users mailbox or archive.

What happens if you don't tag an email?  Is it up to the user to tag the email for Archive to work or is it that all non-marked are archived.  I just want to make sure that when we take PST away that their mailbox isn't hitting the size limit because they aren't choosing to assign a policy on their end.  I want to make sure Archiving happens.

Do you experience users getting to the 10G quota?  I am wondering what others do i.e. if retention policy is 7 years do you grow the archive box or periodically remove/backup data and remove?

The default policy tags messages, if you allow your users to tag messages then this tag takes precidence over default. Examples of which would be Personal Dont Archive and in which case an auto delete policy can remove these from exchange.