There's been some speculation...
Doctor Who has turned into something of a soap opera. Although there are elements about this that make me uncomfortable, it is done well, and we see the characters with much more depth than we did with the classic series.
The downside is there's less time for geekery. Gritty soap operas can't really go through their normal motions when polarity of the neutron flow is being reversed, propulsion systems are being explained or the political welfare of a distant planet is falling to bits... But there is a good balance, only slightly more in favour of soap over sci-fi for my liking, but I don't really care. It means the show is getting good viewing figures and will stay on the air for a long time to come.
In the distant future (perhaps) - what will happen to the show when Russell T Davies jumps or is pushed?
I do like the fact, though, that we get to see inside people's heads.
At the end of School Reunion, Rose seemed quite willing to have Sarah Jane on board the TARDIS, though her reaction to Mickey staying with them was classic... Perhaps it was because Rose and Sarah Jane had bonded. There was some mutual understanding between them. Sarah Jane knew what Rose was going through now, and Rose knew what had become of Sarah Jane. Mickey just gets in the way between Rose and The Doctor.
Rose now knows that there have been countless companions before her and there will be many more after her.
Rose had that confirmed in The Girl In The Fireplace.
I don't think it will be Mickey's presence that inserts the final nail into the coffin of Rose and The Doctor's relationship. I think Rose will come to see The Doctor as fickle and bugger off. There will be no smooth parting of the ways this time. No-one ever leaves on good terms in a soap opera.
Official Doctor Who website