Some other Labour bloggers have reacted a little bit hysterically to Thatcher's visit to No10.
My take is:
a) Personally I felt nauseated, but I'm a Labour activist, not a swing voter, and I guess a lot of people who voted Tory in the '80s and Labour in the last three elections - i.e. the people who decide whether or not we get a Labour government - still respect her (and are grateful if they own their right-to-buy council home etc.) and will see this as some kind of implicit endorsement that it is OK to vote for Brown
b) It helps put pressure on Cameron.
c) Protocol - and sheer good manners - dictate that Brown has to be civil to his predecessors as PM - including the Tory ones. This is in the same league as having to work with foreign leaders like Bush and Berlusconi - because they are/were leaders of our partner countries, despite the fact they would be our political opponents in domestic politics. I can remember Wilson and Callaghan being invited to events at No10 by Thatcher, despite her having attacked everything they stood for.
d) Time is a great leveller. She made life very miserable for millions of the poor, the unemployed, miners, you name it - now she's a not very happy and visibly frail woman whose political legacy has been to see her own party shattered and in the wilderness, and us running the show for 10 years. I think we can afford to be magnanimous - it doesn't mean we are forgetting or forgiving Thatcher's politics.