"roommates online" will lead to "roommates" with time, links and more links and a structure with content based around that term. In your case I believe it is not enough links and enough time. Gradual growth should get you there from what I see...
I've just received some anonymous feedback and a comment for this thread: "If your site was in it you would know it exists. Easy to claim everyone is mad just because you can't see it." It would be good if people could sign off their feedback, so you know who it's coming from. Anyway, my response: I never said that "everyone was mad". I just gave my theory on the Sandbox since everyone who comes out of the sandbox claims to miraculously come out overnight. And just fyi, my sites are also nowhere to be seen in the SERPs. I have a PR3 and a PR5 site. I would have expected the PR5 to be in the top 100 (at least) for some terms. But, it's nowhere to be seen. So, I am still going to stand by my theory until Google perform an internal PR update. As, IMO Google have updated the toolbar but not the internal PR as yet. So, I do believe that "coming out of the sandbox" is just a matter of having a high enough PR and a high number of IBLs as compared to your competitors for a given keyword. If you are high enough, you're out. If not, you're not. This is why websites might have to wait for 2-3 updates (quarterly) to come out. This would explain the 6-8 month waiting period.
It depends on factors such as what sites are linking to you, what their content is about, how they link to you and so on. It is very hard to explain but as long as you keep plugging away with roommate related sites, you will get the terms you are trying to get. My focus would be on natural growth. Let's say you are the best website to find roommates, roommate search, roommates online. That would mean a ton of web sites will link to you such as student sites, appartment rental sites etc. The best thing to do would be to get links in ALL variations such as "search for your roommate", "find a roommate online", "roommates in Los Angeles" (linking to the L.A. page on your site). You should cover all bases possible and that is how you will reach the broadest base of web surfers. Don't nitpic on specific anchor texts too much, just get the links from good semi-related pages of good sites and have some roommate related text on and possibly around your links as well. Mike
Site Tutor has an interesting theory. But which takes longer? To get into DMOZ r to have the site go through the sandbox period.... At least if you are getting links from other sites, those links can be busy driving traffic to you, even if Google is not. I would still prefer to go through the SB than to wait on the whim of a DMOZ editor.