A recent subject line research article by Return Path identified that "click-through rates (CTR) for subject lines with 49 or fewer characters were 75 percent higher than for those with 50 or more." - Source
Ok, before you go subject line chopping to drive your total character length to 49 characters or less, know that a short subject line alone won't guarantee you success. You'll have to test subject line response rates just like everyone else to truly determine what works for your list and niche.
Most email clients cut off the subject line length at 55-63 characters and yes, spaces do count as does subject line header info (such as: [Ezine-Tips] takes up 12 characters before I even begin to write my subject line ).