I upgraded to 1.2 the other day, and am quite dismayed to see that deleting a user will still delete all the posts made by this user. Personally, I find this very impractical, and I hope to see this changed later, so that all posts would remain even if the user is deleted. On the same token, perhaps something along these lines would also work nicely.
Under the "Users" tab, allow the administrator to click on a user's name to display all posts and comments made by that person. Then perhaps, a check box list of all posts the administrator would like to delete (like mass editing) with an additional "select all" button.