Alignment? Something more serious?

I have a 2005 scion tc with nexen N3000 tires that are about a year old. I have them rotated every few thousand miles. I've noticed in about the last month or so that I have lost significant tread on the front tires and my car pulls a lot when I'm driving, even at slower speeds but doesn't feel typical of the cars alignment being off. it is front wheel drive and the back tires have pretty much maintained their integrity...I'm taking my car in to have it looked at tomorrow but I just wanted to see if anyone out there had a simple diagnosis to ease my mind for the time being based on this information...am I safe driving?