HELP--Address in passport renewal

I need to renew my passport since it's going to expire within six months and I've got a trip back to MN in three weeks.

I am not sure what I should fill in for the address? Should I just put my London address on the application for a U.S. passport by mail? I just want to make sure I don't screw anything up since I am going to be traveling soon.

Also, is it cool to keep my visa in my expired passport and carry both? I've read on here that people do that and I just wanted to make sure.
Cheers!!
xoxoxo

How to renew from the UK: http://www.usembassy.org.uk/cons_new/acs/passports/renewal.html

Use the address that you are currently living at. If you're travelling in 6 months then you should be just fine. Just make sure you send the application to the Embassy renewal address with a special delivery envelope for them to return it in. Currently it is taking 15 days to process & issue passports.

You can carry both passports and not have to pay £165 to have it transferred.
http://www.ukba.homeoffice.gov.uk/ukresidency/transfervisatopassport/

You can choose not to have the residence permit transferred to your new passport. In that case, you should carry both your old passport and your new passport when you travel to the United Kingdom, as evidence of your resident status. If you cannot produce your original permit, you may not be allowed to enter the country.