- SFK (min 10) - i think the toons can get xp from anywhere in the instance (haven't tested though)
I believe this is true. Whenever I've done this, I leave them at the gate that lets you see into the courtyard.

- SM Armory (min 20) - You can take your toons at the first stairs after the courtyard and they will get xp even if the booster is almost at Herod (just pull herod out a bit)
I take them a little further than that...into part just before the second set of stairs.

- SM Cath (min 20) - Just keep your toons in the entrance halls, just before the opening on the courtyard, and fight Mograine and Whitemane just outside the catherdral entrance.
/agree

- Uldaman (min 30) - dunno, seems like the toons would need to follow all the time

- Sunken Temple (min 35) - I think i read that near the entrance portal (where the 4 stairs start basically) is a good spot, and fight bosses near the middle of the instance (close to the hole). anyone confirm?
Why bother? Stick in SM till 40 then head to ZF. It only takes about 2 runs to get 40-45. Depending on what class you're using to boost, this instance isn't too bad. I use a demo lock, so I just run and dot with the toons on follow. The dots do a fair bit of damage on their own....and the demon finishes everything off pretty quickly.

- Scholo (min 45) - seems like having the toons on first bridge near the entrance cover a maximum of xp in the instance. anyone confirm?
Confirmed, I park mine on the landing that looks onto the large room at the start of the instance.....they get all XP from the instance kills. Make sure to put loot on FFA for getting the key off Ramstein though

- Strat (min 45) - dunno probably near where the baroness is?
Because of the Eye of Naxxramus, I wouldn't ever risk leaving them anywhere. I used to use Strat as my 45-55 run, but since trying Scholo.....Strat's been given the boot!

- Ramps (min 55) - dunno, seems like pretty much anywhere in the instance
I leave my guys just at the start of the bridge. You're as well boosting them in here till at least 60. You'll get the bonus rep with Thralllmar, plus the XP from quests will go further.