And Diehard isn't that great either. The only time it kicks in is when you'd be unconscious, or in other words "out of the fight and alive". Most of the time, continuing to fight under those circumstances puts you in grave risk of actual death. Not to mention that, past lvl 4 or so, the chances of hitting that relatively narrow range is not huge. It's a better feat than Toughness I suppose, but that's really not saying much.
A +3 is not going to matter much in most cases. If you haven't already invested in that skill, it's not going to get you a reliable success. And if you are investing in that skill, there are plenty of ways to boost it. Masterwork Tools are 50gp a pop for a +2. Boosting skills is not "expensive" in game terms.And 5 points for Skill Focus is really really low, considering how SF lets you do everything from giving a Fighter/Cleric/etc. a decent check on one more skill than he could afford, to having your already-skillful Rogue bust the Level 1 skill cap by almost double. I would have way too much fun being able to buy two Skill Focuses for the price of one feat.
The attack penalty on Manyshot is simply too high. The range is too limited. And because it's a "volley", you can only apply precision damage (Sneak Attack, Skirmish, Favoured Enemy) once. Manyshot is not a good feat, and it becomes worse as you level and your full attack routine improves in comparison.Also I don't think SKR was far off in pricing Manyshot at a 12; it lets you get extra attacks and that's always going to be a fairly big deal, if only because you trust your luck.