PackOfDusters beat me to it, but I'd also say it's not a good thing for most current residents if property prices in SE23 rise above the rest of London.

I've lived in HOP since 2001, bought in 2005 and am looking to stay in the area but move from a flat to a house sometime soonish, however I'll potentially be out-priced.

Evan Davies wrote an interesting article which talks about this back in 2004(!) and it's still relevant I think: http://news.bbc.co.uk/1/hi/business/3701070.stm

One of the main things that attracted me to HOP was that it's a down to earth spot, so personally I'm hoping the new Overground won't change the character of the area too much. Also, if it does bring with it a Tesco or Sainsburys metro then Honor Oak can pretty much say goodbye to ever getting an independent butcher or green-grocer.

Given that there seems to be barely an area in SE London which hasn't had the phrase 'up and coming' applied to it I won't be holding my breath that we're the next Herne Hill or East Dulwich, despite what our local estate agents are saying.