Its always better know about your neighbor websites, hosted on your Webserver/ Shared IP. Shared hosting is good in many ways for service providers as multiple website can be hosted on same webserver under the one IP address. But Some web hosts put many hundreds of websites under one IP address. If few of your neighbor sites are using high CPU resources, It can slowdown the speed of other sites too. Webserver remain busy serving the resource hungry sites and the overall response time get increased. So always ask your webhost about how many sites they host on one webserver. Here I am providing you a link, from which you can check that who else are in your neighborhood.

Reverse IP DNS Check Tool: http://www.myipneighbors.com/

This tool will find other domain names hosted on your IP address. Just enter a domain (www.example.com) or an IP address (127.0.0.1) to get a list of domain names that share the same IP address. Though Its not a perfect method to know about how much load a webserver has, Because Servers cab be configured to host multiple IP addresses. Means Thing can be worst like below:

So you can never Know how busy a webserver actually is. Lesser the sites hosted on a server, Better will be the performance of webserver. Do Remember, If you have Bad neighborhood, it also affects your Google Page Rank and visibility in some search engine listings.

Related Tools:
http://www.domaintools.com/reverse-ip/