It varies WIDELY from day to day, project to project, etc. I have days where I produce no code at all (often doing misc paperwork), and other days where I code 6-7 hours per day.
Lines of code is pretty meaningless as a metric, since different languages can express different amounts of logic in a line of code. Additionally, depending on the type of project I'm doing, I can sometimes copy hundreds of lines from an external source, do a regex search/replace, and have hundreds of lines perfectly good code.
I would have to agree with WingedPanther. I have coded for 12+ hours in a day because I was just so into it at the time... Other days a few hours if any at all.. It really depends on the situation.. However, I guess you would be referring to what we are all presently doing in our lives. In which case, I am currently programming on average 6 hours a day. I am trying to get back into the feel of web design and actually develop something on a professional level. I am currently studying HTML5, CSS3, JQuery, JavaScript, and PHP.... It's a lot to juggle. Hopefully I can do it xD
Great to be back in the field.