1) Job and apartment search -- or "matching." I know there are all kinds of places where you can look for a job or an apartment online. But the process
sucks. There is a ton of information out there, most of which is irrelevant, and the tools for sifting through it are terrible (I'm looking at you, Craigslist). Even when you find a job or an apartment you want to contact someone about, it's a total crapshoot as to whether the person at the other end will get back to you, most likely because they
too are being inundated with irrelevant information -- inquirers or applicants they're probably not interested in.
I can envision something that works more like a dating site solving these problems. Both parties put in descriptions of themselves and criteria for what they're looking for in a potential employer/landlord or employee/tenant. Then the site matches people based on these criteria and sends both parties a list of good potential matches. Et voila -- a much smaller, more relevant set of data for both parties.
I know there are sites that already do something like this in one domain or the other, but I haven't seen any that really do a good job. I also think there's huge potential for putting the two problems together, since people are often looking for both a new job and a new apartment at once, and they use similar criteria (e.g., location, proximity to XYZ, seeking someone who has or wants XYZ...) that are currently difficult to search by.
Edit: I see that "dating site" and "Craigslist competitor" are both on the original ideas.html. I see my idea as an instance of these.