ffmpegx definately doesn't (in Activity monitor you can get it to show both cpu's separately). However, you *can* run two ffmpegx processes simultaneously, and it'll cap both processors pretty close to full.

Most photo stuff seems OK with both processors, (Bibble Pro, Lightroom, etc.), and that's about all I do that's processor heavy.

Handbrake is pretty good for SMP.
Aside from that one, there really hasn't been that much that's needed to be highly multi-processor efficient.

I mean, there is the obvious ones like Maya and Photoshop, but I think that you were looking for less specialty apps.

@bpeoples: how do you make activity monitor display multiple processors? Are you talking about the four-columned graph?

Also, is there a way to launch two instances of an app other than using the terminal?