There was a lengthy discussion about over/underpowered classes a while back, and quite a few people said that the Borderer was underpowered.
Well of course, the Favoured Terrains are a very obvious instance of the GM permitting of denying class bonuses.
The Borderer does get some extra feats and his fighting styles, but what he _really_ shines in is Tracking and Guiding. "Three days' and nights' pursuit… no food, no rest, and no sign of our quarry but what bare rock can tell."
That's the kind of situation you need a Borderer for, pursuing a fast mark through difficult terrain. He can increase the party's speed and follow the tracks at the same time.
However, ingame opportunities for this are of course limited. Except if the party specializes in Bounty Hunting -- that might actually work.
Combat-wise, the Borderer can benefit from some multiclassing. Two-Weapon Combat is not as bad in Conan as in D&D, and it gets a lot better if you have any extra damage sources - specifically Sneak Attack. Flank your opponent and dish out up to eight attacks per round with 2 to 4 extra damage dice per attack, and your target is in a world of pain.
(For instance, Bor12/Thf8 for BAB +18, Dual Short Swords, +4d8 Sneak - with Finesse that's a potential 40d8+STR damage per round, and 5d8+STR are very likely to exceed the magical 20 points.)
Defense is a weak spot of the Borderer. He doesn't gain Uncanny Dodge or the Mobility Chain, he doesn't have a good Dodge or Parry track, he only gains Reflexive Parry very late, at level 11, and that doesn't protect him from getting flanked, but all the same he is forced to use no heavier than light armour. THAT is the real weak spot of the Borderer, if you ask me.
The only class in fact that none of my players thought was worth playing was Borderer.
Nonetheless, my players aren't shy of playing Borderers in general. When we started our group we had a player who absolutely wanted to play a "Hunter" style character, and he chose the Borderer as most appropriate. Then unfortunately, he had to drop out of our group due to a new job, and we hired a new player. He had a look at the classes, hesitated a bit between Soldier and Borderer, and then also chose the Borderer. Mind that I didn't push either player in any direction, because there's also a Barbarian in the party that can fill the "Wilderness Guy" niche very well.