You are getting more than 8 connections because Bitcoin now supports uPnP, communicating with your router and automatically configuring port forwarding, so you are able to make a full network connection, also allowing inbound traffic.
Just as you had to download 5GB of blockchain from other peer-to-peer nodes in order to use Bitcoin, Bitcoin is now sharing your copy of the blockchain and relaying transactions to others.
Bitcoin has no native rate limiting, although here is a thread discussing third-party solutions:
https://bitcointalk.org/index.php?topic=100779.0