I am not sure about whether or not there is a limit, however, why would you try and put so many characters in your title tag? Certainly your keywords would get watered down. Additionally, IE and Firefox only show so many characters in the <title> tag.
Look at the top of your current browser window you reading this post in. That is the Title text being displayed. What do you what there and what is the size of your viewers' window? 600, 800, 1024, 1680?