Also fair to point out that in the first year of the revived series, the Doctor was Christopher Ecclestone. I enjoyed series one immensely and remember the disappointment at hearing that Ecclestone was leaving and that "Casanova" was to replace him... in fact, the regeneration was part of what gave series one it's dramatic structure and climactic ending.
But I want to end this post firstly with the point that with the 2009 special episodes with Tennant still to come, I'm actually talking about an event two years ahead as if it has just happened - how apt. Secondly, I'm just reflecting on how much I've enjoyed from the Tennant years - for instance right now I'm thinking of the thinly veiled references to Douglas
Adams (the dressing gown in the Christmas special, the 42 episode, the Starship Titanic episode...)