A while back, I posted about the appropriateness of using portions of meetings fees being donated to help with hurricane relief efforts. This morning, I read Katrina Relief: Do Good Deeds Make Good Publicity? in Chief Marketer, which explores the issue a little more. As with everything, perception is key—Home Depot can probably do it and people will take it in the right spirit, where Enron donations probably would be looked at cynically. They also suggest giving staff time off to help with relief efforts, rather than tying efforts to sales.
One type of effort I personally dislike is companies that are letting their employees donate their vacation time pay or other bennies to those in need, without adding any matching funds from the company. But maybe that's just me.