Check out the case study on 2 sites--one uses a long keyword/keyphrase, another uses a much shorter keyword/keyphrase. http://www.highrevenue.com/seo/google-ignores-long-link-titles Interesting results. Also, there's internal link testing to validate this theory. Have you seen the same results?
Have you experienced this as well. I see this being an issue mostly with longtail keywords. However, there's a workaround using LSI (Latent Semantic Indexing) content.
First I've read of this but it does make sense. I know on all of the softwares we support, we check to see how the title tag is built. On a number of them, the site name comes first followed by the page title. Usually for us, we flip that around as the site title is in the h1 tag already and given weight. We flip so the papge title gets some credit as well. (Does that make any sense? I'm tired...)
the best way I've seen to dictate title tag length is to copy those that are at the top or at least the first page of google. I ALWAYS see some site that wants help with their SEO and they have a "Bigillion" (yes thats a real number) keywords all stuffed in there. They NEVER rank well. I keep my title tags to nice three keyword phrases with my main keyword first thing in the title. BUT again the best way to see what the search engine is liking is to see what they are already putting at the top. AfterHim.com has a good point (to a certain extent) you want to do both if possible. You want to have the title tag gab the readers attention as far as intrigue and the search engines interest as relevancy.
I usually keep my titles well under 55 characters anyway, I typically shoot for a three word title (the keyphrase I am optimizing for). One thing to keep in mind is that many links you receive organically will have your title as the anchor text, so always try to limit it to high value keywords so that these become high value links.