Although the analogy between gravity and electromagnetism made by David is fine and self-suggesting, it must be cautiously added that there is no proof that gravity must look like exchange of gravitons at the microscopic level. We actually do not know what the microscopic picture of gravity is, and it might turn out to be very different from the familiar description in terms of particle-carriers of that force.

For example, earlier this year there was a preprint by Erik Verlinde suggesting that gravity might be an entropic force. It this is true, gravitons do not appear in this picture at all. This preprint is being actively discussed (more that 100 citations this year). However it also must be said that Verlinde's suggestion still remains a suggestion, not a theory, as it relies on some murky heuristic arguments, not a solid mathematical theory.

Although the analogy between gravity and electromagnetism made by David is fine and self-suggesting, it must be cautiously added that there is no proof that gravity must look like exchange of gravitons at the microscopic level. We actually do not know what the microscopic picture of gravity is, and it might turn out to be very different from the familiar description in terms of particle-carriers of that force.

For example, earlier this year there was a preprint by Erik Verlinde suggesting that gravity might be an entropic force. It this is true, gravitons do not appear in this picture at all. This preprint is being actively discussed (more that 100 citations this year). However it also must be said that Verlinde's suggestion still remains a suggestion, not a theory, as it relies on some murky heuristic arguments, not a solid mathematical theory.

Update: the commenter below correctly points out that regardless of the microscopic theory the large-wavelength gravitational waves exist in any case and they can be quantized giving rise to gravitons. So, I guess my caution was misleading.