Coachie has written a list of notes from a report "Key lessons for marketing in a recession".
I can't say I agree in full, there are some typical marketing self-esteem lies to approve marketing existence. But for sure I agree that companies which cut marketing budgets are long term marketing losers. It was always easier and cheaper to maintain customer relationship rather than building them from scratch.
And of course, crisis is a great time to search for an opportunity and to use new alternative media which is cheaper than traditional one.