Gamebanshee has an interview up with Chris Avellone where he details his and Obsidian's potential Wasteland 2 involvement:

Currently, it’s just me, and I would potentially be assisting with narrative and area design, as well as conversation editor suggestions and structure. Ultimately, we won't know the final logistics for a short while longer, but we'll keep folks updated - right now, it's solely design content work, which is one of Obsidian's strengths.

Beyond that it looks like they will be sharing the tools and development experience they have from years of working on complex RPGs (something inXile really hasn't done before). And he emphasizes that is still very much Brian Fargo's and inXile's game, they're still fully in charge, and Avellone and Obsidian will just be assisting them as requested.

Edit: Oh, and while it looks likely the Wasteland 2 Kickstarter will reach the $2.1 million goal for Obsidian's involvement, there still is a way to go, so please consider pledging if you're interested in the game or want to support Obsidian. The more money they get up front, the bigger the game will be when it comes out.

Avellone is a really good writer that I think will benefit the game in the end. Wasteland 2 is going to be a solid experience from the looks of how this is going.

Totally on board with this. If there's anything Obsidion can do, it's writing.

Everything surrounding Wasteland 2 continues to be awesome.

this whole thing is just the coolest thing ever oh my god

Another interview about it, from RockPaperShotgun.com, this time with Brian Fargo:

And the thing about Chris [Avellone] is that he’s hyper-passionate about Wasteland. For him, it was one of the seminal products that got him into the industry, developed his love for roleplaying games, so I think it’s really kind of a dream for him too.

[...]

What Chris brings is this wonderful density to his levels. So he’ll be involved with the overall, but he’ll also be given some sections in particular that he’ll be able to put his stamp on. It’s sort of like in science fiction novels where multiple authors get involved and do their own parts, all with their own style.

To me, it’s going to be cool because it’s going to give a greater sense of variety as you move around the world. But there’s no way on Earth this is not going to be a sandbox type game.

Get in there Rorie!

Now that the goal has been reached, RockPaperShotgun.com has another interview with Avellone:

Brian’s leading the charge on that. I’ll be the one from Obsidian contributing, and as such, most likely in area/narrative design capacity. In addition, we’d be sharing our knowledge of conversation tree mechanics and layouts with InXile to make conversations in the game as good as they can be. We’ve had a lot of victories over the years that we’ve incorporated into our designs, and we’re eager to share them to make Wasteland 2 even better.

Furthermore, if there’s elements of the tools or other functionality that might help with Wasteland, we’d be looking into those aspects and sharing that knowledge as well (Here’s how we structure dialogue systems, here’s how we’ve set up the tools and editors to do X, Y, and Z, here’s some things that aid with script tracking reactivity, etc, etc).

Ultimately, it’s still early and we won’t know the logistics for a short while longer, but we’ll keep folks updated. Right now, we’re definitely on board in a design capacity, which is one of Obsidian’s strengths.

I just hope that the game will be different enough from Fallout, but then again, if it's not...more Fallout!

@TheDudeOfGaming: There will certainly be similarities, but Wasteland does have a number of clear differences, like being party based from the ground up (companions in Fallout 1 were a last minute addition) and being more rooted in a gritty 80s vision of the future, rather than Fallouts 50s-60s "science can do anything" optimism.