The thing I hate about cigs is that sometimes I can go for days without one - then I'll get the biggest craving ever for one, and can easily smoke 10 more or less one after the other. May not sound like a lot to some people, but for me its a lot seeing as I only smoke that amount a day - let alone an hour! I think I can control my cravings relatively well, as I've been smoking since I was 14 and I'm now 18 and a half, and have'nt been increasing my nicotine intake for the past year or so. Also I smoke B&H Silver, and they contain very low amounts of nicotine and tar (unsure about the carbon monoxide levels though).
Plus theres the 'ghost nicotine' where you have a cig and don't feel replenished in the slightest way possible. So you have another... and another... and another... and another...

Until all that nicotine suddenly hits you at one. Major headrush, usually followed by a visit to the sick bowl. Cigs are bad, full stop. But right now I'm just not at that point in my life where I feel like I need to quit - something no doubt I'll regret in the future, but I live for today and not for tomorrow.