I played a VoP cleric of Fharlangn (I can never spell that) with the Travel domain.

I had a lot of fun with the game, but the DM and I talked about what was expected. I relied on my party members to cast spells on me (as one should), and I cast spells as appropriate. There are a number of exalted feats that work well for clerics (especailly some of the other vows, if you want to play that kind of character). He also had a house rule at later levels that I could take divine feats from Complete Divine as bonus feats. It was a good house rule, and fell within the idea of VoP.

I wouldn't say I was overpowered, but I tend to be a bad judge of such things. It was a small group, which means we all had to be a little more optimized.

I wrote up a few various levels of VoP monk, just to see what he could do, and without party support, it was ok. As was said before, if you want to play that kind of character, do it, but if you are looking for optimization, try something else.

I can see the benefits of a VoP Druid, but it seems that they are just riding the CoDzilla train. With WBL or even a mid to low-magic game, a Druid can probably do better with items.