Regarding my views on Skill Focus: Concentration.
I tend to be the DM. This probably affects my friends views on this skill. My campaigns start from low level, where bonuses to Concentration are important. I tend to enforce rules like concentration checks while casting from horseback, or on a shipdeck, or while swimming, or in a storm. As a matter of course intelligent enemies will maneuver so that spellcasters cannot just 5 foot step out of all threatened squares. Archers ready actions to interrupt spellcasters. Even other spellcasters do this. I feel that these restrictions on spellcasting were intended to balance spellcasters and fighters, so I use them a lot. And it makes fights more interesting if they're happening on horseback, shipdeck, swimming, or in a storm, instead of just on featureless planes with gridmarks on them. So its possibly my DM style.
My players don't mind it so much because enemy spellcasters have all the same restrictions, and usually less optimized builds.
But regarding Weapon Focus, this feat is indispensable. Just like power attack is not as good as people think because they don't get the math, weapon focus is better than people think because they don't get the math. Would you take a feat that read, "Increase your damage with your chosen weapon by 10%."? I probably would. If you hit on an 11+, weapon focus increases your damage by 10%. The better your attack bonus the less you get from weapon focus in that perspective, but since your iterative attacks happen at lower attack bonuses, you'll get the benefit back again. And the more attacks you make, the better the bonus becomes. At higher levels characters make an awful lot of attacks. And on top of that it synergizes with basically every other attack feat out there. Power Attack? If you've got power attack and a two handed weapon then Weapon Focus is better than Weapon Specialization- you can use it as +1 attack OR +2 damage. And on opposed checks every +1 is amazingly effective.
The reason most rogues don't use Two Weapon Fighting, in my opinion, is because they're feat starved and most players favor offense over defense. A human rogue gets 8 feats over his career, plus any rogue abilities he chooses to use for feats. The two weapon fighting chain costs 3 feats. That doesn't leave a lot of room to play.