Robert_Charlton - 11:44 pm on Jan 30, 2011 (gmt 0)
The title isn't a monolithic entity that stands by itself. It very much interacts both with inbound links and with text on the page. This interaction will be influenced by how competitive your most likely search targets are, and there's no simple one-way to do things. Your different pages will probably need different approaches.
Getting back to the original question about length... because the visible part of the title also motivates click-throughs, I try to stick to less than seventy characters, and in fact to less than about 64 (roughly what Google's cutoff point is), at least for important information.
I feel that while you can and perhaps should target multiple phrases in a title, a limitation in title length helps you focus your page content and user attention, which is a good thing. Words beyond this cutoff in longer titles do get picked up, and it can be extremely helpful to include some of your less competitive specifics towards the end of a title. For the right searches, particularly with supporting onpage content, including these can get you rankings for queries that might otherwise miss you.
It's perhaps an open question, though, whether having a long title will dilute the effect of other targeting in the title... or now, with phrase-based indexing, perhaps change its meaning.
With regard to traditional keyword matching, word-proximity within a title is a strong factor, so you definitely don't want to separate words that might be included in likely queries with too many intervening words. Obviously, you shouldn't break up main target phrases at all.
As I read Planet13's comment, his thought wasn't to substitute synonyms to for the main keyword, which I agree would be a mistake, but rather to include them as extra vocabulary. I sometimes do this, if it reads right and doesn't seem spammy, and if I think it would help to target additional related phrases. I consider the other factors noted above when I make this kind of decision.
Use of synonyms also raises questions about co-occurrence effects of additional vocabulary beyond your core phrases in a title. I've tended to think they help, but it's actually possible (now that Google is using titles to reflect concepts as much as words) that some kinds of additional vocabulary might change the focus of a title enough that the core phrases are weakened. I'd love to get some thoughts on that one.