Most of the time if not all of the time you are on shared hosting you are sharing an IP address, I was on a shared host for a while and had no problems with search engines. The use DNS to get to your site, I do not see how sharing an IP would matter.
Believe what you will however a shared IP has absolutely no effect on your search engine standings and the fact that a site sharing the same IP as yours gets band will have no effect either.
As sprintserve says, it is just a wife's tale conjured up to sell IP's when they were abundant and it still hasn't died yet.
DBH Web | 2 BUCK HOST | WHT Member Since 2002. | DBH Internet Enterprises. LiteSpeed, cPanel, Fully Managed WordPress, CloudLinux, DDoS Protection, Daily Backups,
RAID 10 Pure SSD, Premium Network, 24/7 Support, 30 Day Money-Back Guarantee. Over 15 years experience in the Web Hosting Industry.
Maybe you can find some more answers at http://highrankings.com/forum
AFAIK you're generally safe with the search engines with a shared IP. There are just too many websites on shared IPs and the search engines know this very well.