I pondered this a while ago, and came up with a variation of it.
All multiclassing results in Gestaulting. If you're a fighter 4, and pick up a level of Barbarian for 1000 XP, You replace your first d10's with a d12 (giving yourself 2 hp), give yourself rage, fast movement, and 2 extra skill points, though your max skill ranks do not increase, nor does your BAB, or your saves.
As you now have a second class, your LA goes up one. So you gain XP as a 5th level character even though you have 4HD. So A Fighter 10/Barb 8 is an ECL 11, as is a Fighter 10/Barb 2, thought the Barb 8 spent an extra 33K of XP to get there, when he could have leveled up at least twice.
Everytime you Gestalt in a new class you add an additional LA. So A Fighter 10/Barb 1/Rogue 1 is an ECL 12. A Fighter 10/Barb 6/Ranger 8/Rogue 6/Monk 5 is an ECL 14.
This does 2 things, first, the penalty for a caster picking up that "cheap" level for 1000XP, is a slower XP gain to get what he really wants, which is higher spellcasting levels. Second, since you're Gestaulting, you're not increasing max skill ranks, or the number of HD, or the Saving throws past their good save maximum, it becomes very expensive to continue in many classes at once.
Now if you went nuts, which of course would result in: BAB +1/level, Skills 8+int per level, All good saves, Tons of Fighter Feats, +1d6 sneak attack every round, Greater Rage, full progression Wizard/Cleric/Druid spells. You'd have about 6 or 7 HD, at the time the straight cleric has Blasphemy and kills you outright, no save.
Regardless, is it better for a fighter to be a Fighter 12/Barbarian 12 Gestault, or a Fighter 20, or Barbarian 20. A Wizard 12/Rogue 12 Gestault or a Wizard 20?