Keywords if used in title tags it is good in the eyes of search engine so it can make the competition of the page with the alike pages and also can connect to what this page is going to talk about and how relevant it is to the website niche. If you are talking about the Keyword and your Title tag has no nothing like keyword in it, it is not solving the purpose which title tag are supposed to.
In this good post Brian has clearly and cleanly stated the importance of keyword in title tag, along with this the keyword should be in the initial words of the title tag. If you want the on page SEO signal to be clear and louder to the Search Engine like Google the keywords only can make a difference. As much as the keywords are relevant to the whole of your SEO efforts thus the presence of it is appearing one by one in my all posts. As title tag is considered to be the second most important factor in determining page ranking the importance of keywords is itself highlighted so if you have keywords equal presence in title tags, content, post title and the domain name. The success of being at the top of search result is higher if you have a original and well written content. Though I dispute the concepts of being overtly cautious of being banging the same keyword again and again but if you are able to quality content the whole trouble of SEO is half gone with the originality in picture.
http://www.youtube.com/watch?v=jHSqLYUPq8w
As per the above short Video Matt shared a great insight on the Title Tag Seperators and do webmasters should follow only _ as the separator or , = : can also work alike. So as per the search Engine while creating title tag the webmasters need not worry about the use of separator and which separator is used any of the separator which looks nice in the eyes of readers solves the purpose of SEO as well. Tell us how you deliver quality content keeping keyword in mind? And what is your strategy to keep the title tags attractive. Moving to the next topic of discussion of this series the next topic is based on Importance of Keywords and Title tags but with a twist in it. Do tell us with feedback on contact us form how you are improving your page ranking with this Super Series on Google Page Ranking and with this topic on keeping keywords in title tag. If you want to share more insights on this topic you can drop in your comments and if you liked the content do share it with your friends. Also would like to know what is the consistency or frequency with which you are writing on the web also how you keep the keywords in the title tags frequently. How much it improved your ranking.