I'd vote yes on both counts.
I've played it as a player, and DM'ed it as DM. I love it. It is one of the most original ideas in gaming. I do NOT find it at all broken. Generally, the PC is more tough to kill, but is less effective in melee combat (and useless in ranged comabt). Furthermore, as a roleplaying tool, the VoP is phenomenal. It allows a character to be something more than just an average adventurer.
For those who say it's overpowered, I'd say check how much treasure you're handing out. If you're handing out less than the appropriate amount of magical gear, then yes the character would be overpowered vs. the rest of the group. IMC, I've had to supplement the vow because I hand out more treasure than standard (I actually use the Monty Cook idea of halving magic costs above level 6). I've increased the character's spell resistance by +10, because everyone else in the party just purchased Cloaks of Epic Spell Resistance (grants spell resistance 40). Even at epic levels, I think the vow is a wonderful thing.
Just my two sparx,
Sparxmith