Gugafanatic, you have to understand that for most of us, it is impossible to watch a player in action unless he starts winning and makes it to the final rounds. In effect, for most watchers, a player sort of springs into existence only when he is available on TV. So it is to be expected that the number of Federer fans would increase after he started winning.
Other than that, drexeler's reason is the one that worked for me. I've been very late in catching on to the Federer phenomenon. I knew about his Slam victores but had never watched him play until late last year (Reason: no TV, no cable
) and consequently, was not a fan. Now that I've watched a few of his matches, his game and general bearing appeals to my aesthetic sense, if there is such a thing. I've never trashed other players, because I don't think it is useful. Since we're mostly just recreational players, there is probably something to be learnt from most pros playing today.
Regarding the debate about his being the greatest ever, it is futile to argue either way. Anyone can think what they like and find the means and the criteria to justify it. Its like the widely publicized but often idiotic university rankings that US News releases every year.