If you are using a shared web hosting plan for your website or blog, probably your domain name / website is hosted with thousands other websites on the same web server ! If your website performance is really bad and running slow, you may like to find out how many websites are hosted on the same web server with your domain, and from there, you can make decision to stay with the current website hosting company or change to a different one.
Here's a tool to find out how many other websites / domains are hosted on the same web hosting server with you- from the website YouGetSignal.
YouGetSignal has a tool called Reverse IP Domain Check, it can do exactly what you want. Go to http://www.yougetsignal.com/tools/web-sites-on-web-server/, type in your website domain name, click on Check, a few minutes later it will give you a name list of up to thousand domain names that are hosted on the same shared web server with yours.
Remember: You can check your competitor's domain name, to see how his website is hosted !