I'll second what Dawn says
(cos I want her to keep my seat!) 
Here's a list of the "proof of living together" documents we supplied in our partnership application.
Flight itinerary for flights together in 2004
Flight boarding passes & eticket for trip to NZ in 2006
Wedding invitation dated July 2005
Car rental agreement in NZ dated April 2006
Council tax bill dated February 2006
Council Tax bill dated March 2003
Council Tax bill dated August 2003 (all tax bills for different addresses)
Royal Mail redirection letter dated September 2005
Letter from insurance regarding joint insurance policy dated January 2007
Gas & electric bills dated January 2006
Letter from Bank confirming new joint bank account dated August 2005
Letter from rental agency dated March 2003
Tenancy agreement dated June 2002
So you can see we didn't send an awful lot (& no photos as I didn't have dates on any!). Nothing was queried.
15 April 2007 - Original application received.
16 February - Ltr sent back saying I'd forgotten OH's passport - doh!
27 February - Application received again .
10 April - Advised application referred to a medical assessor
30 May - Approved
14 August - Passport with visas returned (we didn't apply for this straight away so we had longer to get to NZ in case of a delay)
Sorry this is a bit lengthy but hope it helps someone.
Sal