Hi Kyoto
If you're looking for a neat way to scrape the sources you mentioned (gumtree, rightmov, etc), have a look at yahoo pipes.
There's a great article about creating csv feeds from dynamic content via a combination of google spreadsheets and yahoo pipes.
http://ouseful.wordpress.com/2008/10/14/data-scraping-wikipedia-with-google-spreadsheets/
I have been using this to pull down sports stats from american sports websites.
Good luck - let me know when you are doing the London one. I can leave feedback on two new builds I have lived in.