I have to admit, i'm such a Mike Cohn fanboy lately, but this particular article was definitely a good read.

I just came on board with an organization that's doing the 'start slow' approach, from top-down. There's definitely one or two groups that have had success with agile and now it's our group's turn and we're having issues. Maybe we're too high profile, maybe our architecture is too laden with overcomplexity and brittleness, maybe the team is too big for it... who knows.

If you're going to do it, make sure you have full support from high up in the organization. Get yourself a champion for the cause who will fend off the naysayers to allow you to improve the process. Once the old practices of doubting and hiding come back into play it's hard to keep moving forward as people backtrack on promises, skulk in corners, and belittle others to stave off humiliation or loss of their job.

Most importantly, make sure your customers want what agile is going to give them: High visibility, truth, incremental delivery, a hand in the work. In the end it's about giving the customer what they want.

edit:

as i was reading tonight i stumbled on this very interesting set of articles:

http://kw-agiledevelopment.blogspot.com/2007/09/how-to-implement-scrum-in-10-easy-steps.html