It's a great idea in theory: nice players will encourage new players to play/keep playing (and so should be rewarded), whereas jerks will discourage players from playing (and so should be punished). This equates to a nicer, more pleasurable experience for the players and a more lucrative result for the developer.
The problem is the implementation. Based on my experiance from the beta I'd imagine the demographic to look something like this: 5% Friendly players, 60% Average players, 35% Unfriendly players. Thus, very few people will be getting the game free/free stuff.
With regards to attitude of the DotA community, my theory was that there were elitist jerks in DotA (1) because there was no tutorial, no manual, and no training levels. The game didn't teach newer players how to play - the pre-existing player-base had to; and unsurprisingly, weren't too keen on this. Given that DotA2 is a Valve game, I think it's fair to say that there will be such systems in place and therefore (hopefully) the community will be less polarised and thus more welcoming.
The presence of an XP/levelling system on player accounts will be defining, IMO, since it will separate players of different skill levels - it was very frustrating to be playing DotA 1 with randomly selected players of mixed abilities and this often created further animosity between players. It's worked rather well in Starcraft 2, as well.
Finally, the ability to spectate better players from the main menu and the function to play against bots will both serve to make the whole experience less intimidating for newbies, too.
Based on the experience so far, I'm optimistic.
Edit: there might have been an in-game manual in DotA1 but iirc it was so clunky that I never bothered reading it.
