Quantaray lenses are usually pretty cheaply constructed and the optics aren't that great. For $149 though, you can take a chance that you'll get a good copy and not be out too much $$. It's a good beginner telephoto. As long as it's an EF or EF-S mount, you can use it on an XTi. I'm not sure if anyone else has mentioned this, as I've only read the first and last pages of this thread - but on a P&S camera, even the "pro-sumer" kinds with big zoom - anything above 5-6 MP is wasted. When you start packing more pixels than that onto a CCD sized sensor, you degrade image quality.
