I've been hearing that coldfusion sites don't do well in search engines. I'd like to know if thats a myth or true?
Why do you think like that ? Can you cite any source for that ? I don't see any reason why CG sites can't rank high. I know many huge sites, alexa 1000 of news portals which rank very high. Ofcourse there are other factors also involved for them to rank so high.
It really does not depend on which platform your site is based on, to rank well on the search engines, Just try to make the sites more SEO friendly and there is proper inter-linking between the various pages of the site.
Site made by coldfusion can obtain a good rank and no different compared to other platform. There are many factors using by major search engine to justify your site for relevancy in their algorithm. If your site has too many of dynamic urls (Joomla is another example for this) you may consider to use apache rewrite your urls and make sure all pages has different titles and meta description.