Up until now, I'd never owned a long telephoto lens. The longest lens I used to own was a 50-200, but I sold that several months ago because I was planning on picking up a 55-300 (which I eventually did, today actually). Anyway, one night I found a great deal on the DA*300 right before Xmas (w/ the help of some bing cashback) and decided to jump on it before the deal went away. I just pulled the lens out of the box a couple days ago and I have to say it is quite an amazing lens. So sharp wide open and built like a tank. Doesn't exactly balance well on my Kx though. Kind of wish I had either the K10D or K20D I recently sold (with a grip) to balance it out a bit better.
For what it's worth, I actually do have the Tamron 1.4x Pz-AF that works with the SDM. Tried it out and it does work pretty well with the 300 (a lot better than with the 55-300). Granted I only tried it indoors in a pretty poorly lit room, so I expect it would work at least as well outdoors in decent light.
Originally posted by imtheguy 
Depends on the type of shooting you do. At close range it quickly becomes less than 300mm (due to its internal focusing design, or so I have read) and I find myself using it for 95% of my outdoor shots since many garden shots looked better at 6' with the 300mm than with my 100mm macro lens. It was also the biggest quality lens I was comfortable swinging around on a K20D plus grip all day. Getting it new for under $1k sealed the deal. Lastly, after lusting for the Sigma 100-300mm f/4, I realized that almost all my nature shots to date with a 55-300mm zoom ended up being at 300mm. So I went with the prime.
Just my story, hope you find happiness. Maybe in the form of a 1.4x TC for the lens or something.
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