The Outdoorsman talent has a secondary effect that reduces overland travel time by 50% (and this does not increase with ranks). Does this benefit the group if the character with Outdoorsman is acting as a guide, or does it only apply if everyone moving has Outdoorsman?

I would hope so - it's pretty crappy otherwise. My group hasn't been doing any trekking since I bought the talent, however, so I don't know what my GM's opinion is.

My GM applies it to the group. Since we also use a lot of props, terrain and maps, he some times gives me a little extra ground if I am just short of making a movement to cover, to a different range band, or to an item / thing of importance. Nothing to much really.

The couple GMs I've talked to when it came up have let it apply to the entire group, and I'll do the same should it come up in any games I run.

It's probably another one of the situations where FFG has left it up to the individual GM to decide. Though I agree with Col. Orange that the talent loses a lot of it's benefit if it only applies to the individual character.