[SixOfSpades]

Druids do indeed zip through Levels 1-10 extremely fast, even faster than Thieves. But they are SO DAMN SLOW in Levels 10-15. In fact, in the whole game of Baldur's Gate 2, they only gain FOUR levels. Come on, Fighter/Cleric/Thieves level up faster than that. The reward for tolerating this abysmally slow level gain comes in ToB, when you hit Level 15 and suddenly are up to 6 memorization slots for ALL your spell levels--this is a huge jump from Level 14. Then, each time you level up, you get Druid special abilities, etc.

I'm doing a Totemic Druid myself, and I'm only going to stick around for a couple of the Druid high-level abilities, and Dual to Fighter at around Level 18. For a Druid to Dual to Fighter, you need at least 15 Wisdom and 17 Strength. To go the other way, you need to be True Neutral and have 15 STR, 17 WIS, and 15 CHA.

As far as Fighter->Mages go, the Kensai->Mage is a big favorite. Kensais have the disadvantages of not being allowed to use armor or missile weapons--but they can still use Throwing Daggers/Axes, and if they Dual to a Mage, they can wear Bracers and Mage robes. I might do that next time, but for now I'll stick with a plain Fighter->Mage, kickin' ass with his Bow. Another tactic (which seems a little chessy to me) is to make a Kensai, then Dual to Thief. Thieves will eventually get the Use Any Item ability, so your character will be able to use literally anything--Mage wands, Cleric scrolls, and those cool missile weapons and Plate armors that are supposed to be off-limits to a Kensai.