I forgot the website url. It showed the number of websites hosted under a webhost. Anybody remember it??
Domain tools will tell you the number of sites hosted on 1 IP. They only change you if you want to know which domain names are hosted or parked on this IP.
http://webhosting.info will show the number of web sites on a hosts name servers. Obviously they could have a lot of servers sharing the same name servers though.
It is hard to tell, technically, if the hosting company has back end redirect then there are a few servers behind the shared IP on the firewall. I suggest you setup a uptime monitor to get an idea of up time, of course, it is performance monitor but it is free. Search basicstate, I am using it right now. It is free and it pings your site by HTTP request every 15 minutes also check DNS etc.