Like Tagged and other social networks, Facebook too has added a "mass invite" feature allowing members to import and invite all email addresses from their Yahoo, Hotmail, AOL, Gmail or MSN address book in one click.
This feature may have existed in Facebook for some time but now they are promoting it very prominently on the homepage so Facebook members are more likely to explore it.
Maybe the sole motive here is to increase the Facebook subscriber count but such features are often misused. If are finding it tough to handle the email invitation load from Facebook members, your best bet is to disable email notifications that reach you when someone adds you as a friend on Facebook.
Of course your queue with pending friendship requests will still grow on the Facebook website.
Mass Invite Your Friends | My Facebook Profile