Moderators will see a new 'trash' link in the sidebars of the forums they moderate. Posts that are deleted from now on can be restored from here. There is also a trash page if you filter by 'moderated' on the front page, then click the 'trash' tab, which gives you an accumulated view of trashed posts from all the forums you moderate.
Admins have an additional item in the actions menu of posts: purging, which removes the post permanently. This can only be done for posts that are already in the trash. Also, there is a site-wide trash in the admin menu.
There were two motivations behind this feature:
- Being able to undo mistakes in moderation
- Being able to undo mass-deletions by rogue moderators
The second point now makes it possible to add more moderators without worrying that they'll abuse their positions.
Posts deleted by their posters will not be stored in the trash.
If you have any concerns or questions about this, please let me know.