The categorizing of friends in Google+ was a huge success, else why would Facebook do the same (or almost the same). Strangely LinkedIn has not woken up to this. Not sure if I am the only one having a problem, but once you accept an invitation in LinkedIn you cannot immediately categorize that contact. Very irritating.
Just as in any normal company, we too have many non-human email ids (sales, info, support, help etc.). We keep getting LinkedIn invites to those email ids. There is now way of notifying LinkedIn that we don’t want any invites for that email id. Many social networks do provide you a way to block invites. It is a different matter whether they honor your request for blocking invites (WAYN.com being one of them).
Update (Oct 24, 2011): I see a “unsubscribe” option in LinkedIn invites today. Thank you LinkedIn.