I had one a few years ago - made the mistake of trading in a pair of kit lenses from a film kit against it.
For convenience, it was great - no need to wonder if I had the right lens on, it covered a lot of bases BUT... the distortion at both ends was very noticeable (OK, that can be corrected in PP but takes time and effort - and I was using film so not as easy) and it was as sharp as a spoon anywhere over 250mm. As soon as I also got a DSLR, I found I was using the 28-300 for almost nothing but missed the reach so bought a 70-300VR to partner the kit 18-70 (Nikon).
If you only ever want prints up to 7 x 5 or web use and aren't bothered by the distortions then go for it, if you want bigger prints and straight lines near the edges, think again. (The chap I flogged mine to is [AFAIK] still happy with it on his D50)