No one attends talks !
Ok, that's a little bit of an exaggeration: but between "conference = journal in a hotel" and "chicken chicken chicken" it's fair to say that talks at conferences tend to draw only those who are particularly interested in the specifics of a work, and is less likely to draw casual attendees.
A poster session on the other hand is like wandering through a nice bookstore: you can browse the topics as you see fit, and jump into anything that catches the eye. If you're a poster presenter, this is a great opportunity to convey a higher level intuition for your work to an audience that might not be conversant in the specifics
It's all about the eyeballs !
Everyone should make posters ! We are in an attention-based economy now, and your work gets known and disseminated only if you can get people's attention. A poster is an extremely effective way to communicate with your audience, especially if you use the visual medium effectively. Most conferences now have elaborate poster sessions and it's a great way to meet people and hear about material I wouldn't have otherwise had time to assimilate.
It's all about the networking !
If you're a student, either presenting (or better yet, not presenting) at STOC, what better way to get conversations going with more senior researchers, instead of huddling together with your fellow students, wondering if you can make enough eye contact to get an intro (yes, we do notice :)). I can almost guarantee that you'd have more meaningful interactions with researchers at a poster than at a talk where people have half an eye on their email.
It's all about the impact !
So you got a paper into STOC ! Congratulations - there's a nice CV bullet for you. But what's next ? You want people to read your paper, talk about it, argue about it, and build upon it. Don't you ? Again, a well designed poster can draw in attention much more effectively than a talk in our attention-deficit world, and more attention means more discussions, and more potential impact.
It's easy !!
Now you surely don't believe me :). If you don't. consider your options. You can use LaTeX/beamer, and here's a fantastic resource to help. You can use Powerpoint or Inkscape, or if you're one of those fancy Mac people, you can use whatever fancy Mac tools I'm not cool enough to talk about.
Best of all, you don't need to have the poster ready by the deadline of Mar 31. All you need is a short abstract.
So don't think ! Whether you have a paper or not, do consider submitting a poster - by Mar 31 - to firstname.lastname@example.org - and here are the details.