The majority of SEO experts agree that Google places little value whether a site is hosted on a shared server. The only risk noted is that of a spammy site hosted on the same server may have ill effects. None the less, Google has no issues and I can attest to that with some great results had on shared servers. Yahoo, on the other hand might be a little more of a pain when it comes to this. I have one particular site that is really taking a long time to get indexed through Yahoo. Yahoo has a site manager much like Google Webmaster Tools. While a website will usually get indexed in days on Google, I have been on hold for about a month now with Yahoo. After doing a little digging around, I found this little post on the Yahoo SiteSearch Discussion board. It seems another user is having the same issues and a Yahoo representative responded,

I’ve been looking into this case and have identified why your site hasn’t been crawled yet.
Basically, we haven’t been able to crawl because of the number of other sites hosted at your hosting provider and the limited number of connections we can make to their IP address.

I assume your site is hosted by a larger hosting company or is on shared hosting. Usually this means that the hoster will allow many domains to share the same resources, including the IP. What this means to us however, is that we can only crawl a limited number of these sites at a time.

If possible, let me know who you are hosted with and we can *attempt* to contact them and get the situation resolved. I must emphasize that the situation is dependent on them assisting, so I can’t guarantee that it will have a favorable conclusion.

Let me know if/how you want to proceed.

The post goes on without conclusion so far but it seems as though Yahoo sets limits on the amount of sites it will index on a shared server. Just to be safe, if you are on a shared server you might want to try and get a Static IP to appease Yahoo.