Joe Federer: I went on safari with a D300 and a 18-200 and was definitely focal-length-limited at times. But realistically, the times I was focal-length-limited were times when even a 400 or 600 wouldn't have done the job.
I was recently in Namibia and Botswana with a Panasonic FZ150 and an Raynox 2025Pro teleconverter which the EZ zoom gave 1760 (35mm equivalent) and sometimes that was not enough. Also almost impossible to keep steady. You just have to accept that sometimes the image will only be in your own memory and not on a SD card. BTW the FZ150 IQ was more that adequate and so handy to be able to go from macro for dragonflies to that long zoom for rhinos and elephants in seconds.For those interested in keeping that big lens on your fullsized DSLR steady - have a look at this site - this is regular visitors do it http://www.kruger-2-kalahari.com/photographing-from-vehicles.html