I rock a Canon DSLR (an Digital Rebel xTi to be precise) and I absolutely adore it. I am thinking about investing in a 70-200 mm lens for it. Anyone have one? Is it totally worth the money? I have been lusting over it for ages but have never been able to justify the expense. I have a 75-300 mm lens but think that the 70-200 would be a real improvement.