Meredith Vieira interviews the authors of Grave Expectations who were inspired by attending several funerals that did not reflect the character of the deceased.
From the small amount I've been involved in funeral planning for other people, I find it's usually done in stressful, emotional circumstances, and you don't have the frame of mind to really think through what would reflect that person's personality.
If you want your funeral to reflect your own style, I think planning it in advance for yourself is a great way to go. Plus, you can really take burden off of loved ones in terms of logistics and finances.
Also, if you watch the piece, I love the idea of the "vid-stone" ... but would it hold up to the elements?