Not that this will convince Gavin but I'm a rules knob, have played both systems extensively and can offer a little to this discussion.
2a.) Let's start with the rogue.
- They are about the same as before with better skills overall, a couple new tricks and an extra HP/level but with nerfed tumbling. I had never heard of using splash weapons to sneak attack and probably wouldn't have allowed it in my game because I can't imagine a vial of acid being used to do precision damage. That'd be up to the individual DM though but I'd have Rule 0'd that one.
- In my estimation, fully optimized PF fighters are actually better at tripping than 3.5 (after the first handful of levels) because CMB gets every bonus that the tripping weapon gets, including, but not limited to, the bonus on the weapon, weapon focus, weapon training, morale, luck etc. etc. There are a couple of weird cases where 3.5 trippers can do a better job (against flying creatures and when using the arguably overpowered polymorph mechanics to change into very specific creatures) but their chance to trip is better against CR-appropriate targets than in 3.5 for every level except the first 2 or 3 (when the strength check bonus is better). That it costs an extra feat is inconsequential because there are more feats in PF so they are all a little cheaper to get.
- Regarding Power Attack, there is a fallacy there because a PF power-attack optimized fighter gets a better to hit to damage exchange rate (-1/+3) and gets more to hit and damage bonuses through weapon training. Accordingly, while the PF fighter doesn't do as much per hit, he hits much more often against CR-appropriate targets and does the same or more damage per round.
- Armour training means full speed fighters in full plate.
- Anecdotal I know, but the straight up sword and board fighter in my face to face PF group is the strongest PC by far. At level 10, his AC is just now dipping into hit-able range, does way more damage than anyone else and has been this way since the beginning.
- Flurry of blows has a better BAB, more attacks, more dangerous stunning fist at higher level.
2d.) Melee monsters stronger.
- I haven't really seen what you describe to be all that important. The flip side of the grapple nerfing is PCs aren't out of the fight as soon as they are grappled either.
3.) Lots of the more powerful classes were buffed.
- Pretty much all of the buffs are for colour or lower-powered than the spells whose action they replace.
- Sorcerers are a little better than they were because quicken spell works and there are a few interesting options. In my mind, this is a good thing because I always felt sorcs were behind the curve compared to wizards.
- Wizards are about the same because in practise, they do the same things they did before - cast a spell every round. The class abilities aren't much to write home about and either replace a crossbow bolt or are largely non-combat abilities.
- Cleric spells are about the same as or worse than before. Some nerfing in the domain abilities and armour proficiencies have made uber-melee cleric builds less viable than before. Channelling energy makes the cleric more fun to play but doesn't really affect balance because it's a whole-party affecting ability.
- I haven't played much with the APG classes but regarding the witch slumber hex, I suspect it would be not quite so overpowered in actual play. Its major downside is it still only affects one target per round and if the target makes its save it cannot be targeted again. If we look at SOS/SOD spells, at 1st level, sleep is better because of more targets. At 5th level, Stinking cloud hits more targets and is just as bad in terms of taking them out of the fight and Hold Person is pretty similar with the target being unable to be roused. At 10th level, Dominate Person/Hold Monster/Feeblemind are about the same or better. At higher levels, there's just so much better you could do with your time than invoke a single SOS/SOD saving throw.
In my now 10th level PF group:
- The fighter is the strongest PC (but he suffers now that higher level enemies are gaining mobility advantages)
- The bow ranger is the second-strongest (less damage per hit, a lot more hits per combat)
- The cleric, wizard and sorcerer are about equal (but admittedly, they aren't being played to full potential)
- The shadowdancer rogue is the least combat effective and maybe the most non-combat effective underground/at night
We had a bard who was great at support but sucked at direct combat because of his build. He's been replaced by a barbarian who has ludicrous HP and does loads of damage. I'd say the bard was on the rogue tier and the barbarian is somewhere in the fighter/ranger tier but time will tell on that.