Over Billie? Yeah, you're getting older! mind you, the current assistant is a cracker...
Search Youtube for "Catherine Tate Nan"... If you still find her attractive, there's no hope for you and your definitely old!
That picture of Karen is a bit unfortunate you found. Half the spell is her accent though, and frankly, her very first scenes are a bit persuasive...
Torchwood Torchwood: Season 1Torchwood: Season 2
As to... "I'm not sure the Doctor would be too proud of Torchwood", he definitely isn't! On the episode where Torchwood was introduced he made his feelings clear. I believe it's the one where the Daleks are invading and he has to send them through to another dimension? Also, I believe that the original Torchwood was created by Queen Victoria after she met the Doctor. She was pleased he had saved the day as usual on the occasion, but she took him as proof of alien existence and set-up Torchwood to defend the earth, including against the Doctor if felt necessary!
Of course he has softened toward them somewhat, but he'll never completely trust them. Same with Unit who I think Martha and Mickey end up working for? I lose track...
I thought Donna's arc was just sublime and that ending was powerful. Again, they usually allude to a romantic angle with the assistant, but here it's clear, the Doctor is just lonely.
Season 5... is just awesome. It builds on that angle so beautifully and if the ending of this season has got to you, well, you ain't seen nothing yet. Dark sides are explored and considered. I'll put you out of your misery on one score, Donna is back in it, though not in a huge capacity. She is important, but only for one point in the series (the ending of series 4 has not been undermined). However, her grandad, Wilf? Another matter entirely. He has a simple line of dialogue toward the end that will take your breath away... Sorry, I should clarify. Wilf doesn't turn out to be some evil overlord or anything, he is just Wilf, but my goodness. How they employ him in the plot is fantastic.
Oh bugger. Yes you're right, I forgot! Tennant's run was brought to a close in the specials. Sorry for the confusion!