i used one, and stomped ass with it... it is still the strongest offensive skill.. 156 bonus damage and 36% lifesteal that stacks with an orb affect, is good...
I use the demon prince, vamp soul, spiked armor, guardian ward, reincarnate.
It can level quite well... Ive only used it in team games, in a 1v1, compared to an int hero, it cant level as fast.. but i can hit 8 for the first duel in team games. This is meant to be a team game though, so, i consider the build VERY viable... I stomped the yard with it.