I don't think I will ever understand the FICO scoring model. I have been back and forth around the mid to lower 600's for the last year or two. This is mostly due to high util, a couple of 30 day lates in 2010 and credit inquiries.  

I recently applied for a line of credit at the Firestone dealer to purchase a new set of tires, and today that reported as a new tradeline with a $1000 limit, and 0 bal. As a result the score dropped from 615 to 559.. Does that sound normal? Seems like a big hit for just one new account..