Take one harsh look at yourself.
Are you boring? My biggest stumbling block in this arena was because I was, indeed, boring.
There are 6.5 BILLION people on this earth. What makes you unique?
If we hypothetically believe that someone's goal is to meet as many "interesting" people as they can in a day, what's going to make you worth talking to over the next guy?
I used to be really into MMORPGS. Really.. Really.. into them. When you're spending 18 of 24 hours playing video games that no one else plays, you're not going to have much to talk about with people that don't. Talking about the 6 hour raid or the l33t new sword I got didn't mean much to my friends who were studying, partying, and watching TV.
So I either had to find people who
also played video games that much (unlikely, because they'd be just as reclusive) or I have to develop interests and knowledge relevant to the people I like to associate with. To me, it was reading the newspaper - being current on events and politics. Something to mention or joke about. Reading Slashdot and Digg to keep up on tech news - something to talk to with my more geeky friends. Hell, even keeping up with pop culture just so I'd have something to talk about with the silly celebrity-worshipping crowd.
To me, its all about being interesting to the people you yourself are interested in. And knowing something about your common interests is a great way to start.
Oh -- and one thing that helps immensely.
People are FAR more interested in telling you about themselves then hearing about you. Ask people questions about themselves and there will be a never-ending stream of discussion. I think it's human nature to be proud of what we do and who we are, and we love to talk about. Even the most shy people I know will engage and talk about themselves and their goals in a meaningful manner if you ask serious and genuinely interested questions.
EDIT: I went to bed and got back up just to add more to this post. There's really a lot to be said here, and I think its one of the most important skills humans can possess. We're talking about interpersonal skills.
Think about everyone within 10 feet of you at the table. Do you know their names? Their goal in life? Why they're in college? Their plans for the future? Their age? Where they're living? What their major is? If they have a boyfriend/girlfriend? Do they work?
If you don't know any of that, you CANNOT expect that they'll be interested in getting to know these things about you. But it is these little details, these connections with names and desires, that help us bond to people. Maybe they're curious about you too, but they don't want to broach the question. If you're uncomfortable in your place and you want to be an active participant in the conversation, then you have to do it yourself. It's very unlikely that you'll meet an outgoing person willing to drag you into the conversation each time.
Does Mr. PH.D 1.5 like to talk about Physics and Math? Is there any part of Physics or Math that you like? Don't like? Would like to talk about? Any current events in that field that he might have heard of?
And don't be embarassed to ask for a name multiple times. One of my first days of school I had to learn 35+ names because I'm responsible for tutoring each one of the students. Its important that I know their names because it makes the tutoring that much more personal and ultimately effective. And I forgot a few student's names 3 or 4 times. It'll be awkward for about 15 seconds when you have to ask "I'm sorry, I totally forgot your name" but it'll be much more effective than trying to work around ever saying their name.
And if you really need help at the table, you could say something like "You know, I've sat with you guys a couple times but I don't think I've ever gotten your names. I'm (your name here). *extend hand*"
Work on it, becuase making bonds like this is the most important skill you'll gain in college and in life. Who knows when you'll be stuck in Physics and Math and will need Mr. 1.5 PHD to help you for a second. People are just potential friends and potential benefits waiting to be talked to.
