Friends made me watch ONE ep of Torchwood, the one where Jack meets Jack. I was hooked on Jack. So I watched Season 1 of Torchwood. Then caught Empty Child/Doctor Dances on SciFi, and therefore went and watched every episode of new Who that had Jack. Then watched Children of Earth. Then went BACK and watched Season 2 of Torchwood, followed by watching Doctor Who in order from "Rose" on.
:P
Have since watched a few bits of Classic Who...enough to form an opinion of some of the other incarnations of the Doctor.