1) I don't get the idea. Do you mean something like an automatic check-in based on your current location?
2) This is already partially covered by Twitter: just twit "Who wants to meet in 5 minutes in..."? I don't see the need of an added service. Sure, you could add all the features you can think of, like maps. But now twits can be geolocalized too.
3) I like this idea. The only problem is that a system like Aardvark could work mainly for big companies with a large customer support department. Such companies could be difficult to convince to try the new system for their support.
4) Last.fm already does that. Edit: I've seen only now your comment. Well, I prefer the Last.fm model...what is the logic behind an invite only service? If we have in common many favorite artists, it's probable that I will like also some other artists from its collection.
5) I don't own an iPad and I can't judge the usability of its keyboard...but I don't see many people programming on that thing. It's more a consumer, rather than producer type of product. However, I believe there will be hundreds of geeks ready to install it on their iPad, even if they won't use it much.
Thank you very much for your ideas! I'm currently looking for one and posts like yours are really useful for my brainstorming.