It is simple using the exchange management shell to export mailboxes to pst in 2007 and 2010.
Firstly you can export mailboxes individually
Export-Mailbox –Identity ‘alias’ –PSTFolderPath
Secondly you can export an entire database
Thirdly you can export by OU, handy if you have an OLD or ARCHIVE User group in OU you want to archive
Important to note, as with exmerge in 2003, exporting data from a mailbox to a PST file does not delete the content in the source mailbox. If you want to delete the content you have to include -DeleteContent or -DeleteAssociatedMessagesmessages.