When is it OK to Say I Love You?

I've been dating my girlfriend for now six months, and we've yet to say the words I love you. So I started to think if this was normal or if there is something wrong with us. Looking back at a couple of relationships I've had, one ex told me she loved me after only three weeks! Another did it after two months. So now that it has been six months with my current girlfriend and we have not said it, I'm just wondering if its normal or not.

I'll be the first person to tell you that you should only say it if you mean it. After thinking about it, I came to the conclusion that I'm not really there just yet to bring it up. And looking back at my past relationships I think I said it back only because I felt I needed to and not really because I felt it at the time.

My relationship is great right now, we like each other a lot, we both spend plenty of time at each other's places and I can honestly say we go about 50/50 on everything, its awesome! But if things going so great, why not the I love you? Are we becoming those couples that simply go through the motions but in reality there is nothing there? Or are we just being careful by not putting ourselves out there just yet? When is it just too long to say it to the point where you know is just not going to work out? What do you think?