Speaking just for myself, the biggest draw for me is the fact that without virtual online tabletop applications such as Roll20, Maptool, Tabletopforge etc. I would not be playing period.
I live in a very small community in northern Canada (pop >7000) and there is zero interest in any of the pen & paper role playing here. Because of this, the last time I got to play, it was AD&D 2nd edition.
I had pretty much given up, until one of my coworkers from our Division office asked me if I wanted to try playing using an unholy mashup of Skype, and our corporate VC system. I agreed, and started re-immersing myself in the RPG culture, reading rule books, living in /r/rpg on reddit etc.
Now, my little workplace group that we got started was pretty much wholly composed of newbies, and after about a month, half of them quit. I started to get scared that my DnD was going to disappear as quickly as it had appeared. Reddit had put me onto VTT tools, of which Maptool seemed to have the most traction by far in the community.
I decided that I would take up the mantle of DM, and run my own game.
I cast my net and recruited friends & family from across the country until I had a happy little party of 4 players and me. Now, my closest player lives about 800km (500miles) and my furthest is around 1500km(930miles) away, so yeah, without applications like this, there is no game.
I don't think that it'll wither on the vine without social/LFG tie ins, since I'm sure I'm not unique in my geographical limitations. Heck, I'm not even sure I would use them. I'm from Socially awkward penguin side of the geek spectrum, and I constantly worry that I'm a bad DM. Playing with someone I didn't know would greatly exacerbate that to the point where my nerves would probably destroy the campaign.
Now, I'm not saying that they shouldn't exist just because I'm antisocial. I know that for every person like me, there's 5 that are actually socially adjusted, and a lot of people who weren't as lucky as I was finding friends to play with would love being able to find a group.
However, what I think would be better, would be a partnership with one of the already established LFG communities, since every time you split people apart, there's a smaller pool of potential groups to draw from. It's the reason Facebook is wildly popular - for better or for worse, everyone is on it. I can talk to some of my friends on Google+ or I can talk to almost ALL of my friends on Facebook. (I guess that's also an endorsement for utilizing Facebook for matchmaking)
Anyway, I didn't mean to write anywhere near as much as I did; just wanted to chime in with my opinion.
Also, I think what will be the biggest factor in determining the success of Roll20 will be functionality. I've tried most, if not all of the big names (Maptool, WotC's VTT, openRPG) and from my own experience, and a common sentiment I've seen hanging out on the reddit rpg & dnd boards is that what most of the VTT's have in common is they're "good enough" -- they all get the job done, but it's like writing a book using VI or notepad. Yeah, it'll get the job done, but it's not always functional or elegant, and I just want it to work, and get out of the way so we can spend our precious few hours per week gaming instead of doing tech support. I do enough of that as it is.
A funny anecdote:
I originally heard about roll20 in a reddit post by someone from the team (I'm assuming Riley) and I was super excited since the way he talked about it was mirroring my issues with Maptool. More simplicity, less focus on automation/video gamification, more focus on the story and the pen & paper feel. This was before the Kickstarter was launched. I exchanged a couple PM's with him about being a beta tester, and then returned to life as normal.
About a week later I hear about the Roll20 kickstarter. I checked it out, said "This looks neat, but I'm going to pass and see how the other endeavor pans out."
Another ~week goes by, and I see a post about Roll20, and I notice familiar usernames. Something clicks in my head and I realize that it's the same product, so I take a closer look, like what I see even more, pledge, and here we are.
Ok, I'm really done now. I tried to TL;DR this and even that wound up being a couple paragraphs, so, sorry for the monologue.