The power behind Factorums is their insane flexibility with INT to almost everything and, at level 8, taking extra standard actions.
While knowledges are good skills to abuse with knowledge devotion, this is just the tip of the iceberg. They work best with Font of Inspiration feat found in a web article.
1) Int to attack and damage is useful as, especially at early levels, you end up actually hitting and dealing non-trivial damage and at later levels, you can use with effects like manyshot to nullify all penalties while getting extra attacks.
2) Int to AC and saves allows you a few turns of being face to face with the big, mean monster without dying.
3) Int to DEX and STR based checks means you have a bonus to initiative, trip checks, escape artist checks, move silently etc. All of these you can use offensively or defensively.
4) Factotum level to each skill 1/day likely means that you succeed on that crucial skill check. Bluff/Disguise/Jump/Disable Device.
5) You can take obscure skills like autohypnosis and Iajitsu focus.
6) At 8th level, you can emulate spring attack without any feat expenditure a few time per encounter. Move action to move to opponent, standard to attack, use the other standard action to move away.
7) Any standard action attack you can use twice in a turn. Manyshot is fun with this as are maneuvers as are the few low level spells you can cast (True Strike, etc.)
And remember, the inspiration points recharge every encounter.
Because of the flexibility, they end up being the ultimate ninjas. They can play offense in several ways, defense, skirmish, infiltration (just add factotum level to disguise check or INT+Factotum level to hide and move silently), battlefield control with tripping, party face by adding Factotum level to Bluff/Diplomacy 1/day, even minor healing! About the only thing they can't do is cast high level spells at the same rate at wizards. Although they DO get up to one 7th level spell if you take them to 20.
