It is interesting to note that Yahoo! presented @ NANOG a couple days ago they were getting XX Mbps (15? I forget) of ICMP traffic. They mentioned they could use this data in a decision whether to considering limiting ICMP (without actually saying they were considering limiting ICMP).
Ok.. I'm guilty of this as well, in fact my 'network watcher' sent a single ping to www.yahoo.com every 15 minutes until your post. I just turned it off. Now, here's a real issue, many of us probably have similiar systems that ping upstream connections and page/alert/log when there are problems. My 'watcher' could also grab a web page (checking port 80) or do other tests, but I have always assumed that the ping was the least amount of traffic easily and reliably sent to check connectivity. Whats the best way to monitor upstream connectivity for this purpose?