The Wikipedia entry looks okay, at least it fits with what I remember. Anyway:

http://en.wikipedia.org/wiki/Nuclear_fusion

About half the time D+D produces Tritium and a proton. The other half it produces He3 and Neutron. As I recall, very rarely D+D will produce He4 and a gamma.

D+Li6 is a relatively "hard" reaction, and as with D+He3 you will also have some D+D reactions. After D+T, D+D is the next logical step.

Lithium blankets are all very well in a D+T reactor, but design isn't trivial. Neutrons are going to run into other things, like expensive superconducting electromagnets.