I have enjoyed this thread. I like the ideas. But I just have to share what I do. Its slap crazy - but let me explain.
Let me first provide context. I think that one of most difficult chores for a gamemaster is making sure an adventure scenario can be accomplished by the players. If its impossible, that's bad. A self-designed module has to take into account the skills and spells the players currently have to provide the right level of challenge. With a published module, either you have to "hint" the players to take a particular skill or spell (and hence give away something) or modify the module. What's the point of purchasing a module if you have to spend hours editing to make it suitable?.
So. I allow my players to spend DPs whenever they wish on skills and spells they already know, could reasonably know or provide a story suitable explanation why they could know. I allow this to be done even in the middle of combat if a player so chooses - even to purchase a fate point if they wish. I allow them to purchase as many ranks as their level allows per the standard rules. The story rationale is this - the player suddenly remembers they know how to swim or ride a horse. Or secretly have been practicing Turn Undead.
I know it sounds insane - it goes against everything RPGs have ever been. But it has many advantages. Since I encourage players to hoard their DPs until they need them, many new skills are born in the context of an encounter or story obstacle. This gives most skills and spells special story context and history. I like that. It allows players to be creative and actually take relatively obscure skills because the context allowed the skill not to be a potential total waste.
For my many years as a player in Rolemaster (I own a tattered, stained copy of the original Arms Law) and Chaosium games, I was always frustrated that there were all these interesting skills available that I wanted to take - but knew that the odds of any single skill proving useful was practically zero. Still, I would waste a few points here and there on obscure skills and then go through stupid gyrations to try and work the skill into the game.
Instead, this way - during the adventure, the odds of SOME obscure skill being useful is actually quite high. And so players have an incentive to take them when its useful or even critical. Its a nice way to give a character extra color without having been penalized for trying to do so up front. Plus, adventuring teams "balance" themselves out over time without having to do careful planning four and five levels in advance.
Its also a great boon to the GM. Purchased modules can be run practically "as is". A particular skill or spell is critical? Players don't have that skill or spell? No problem. Just spend the DPs, keep going. Self-made modules can be created the way they "should be" instead of trying to make sure the team's skill mix will work. Before I came up with this idea, I would provide an NPC with the critical skill if necessary - but that's kind of like playing solitaire RPG... And mind you, I don't make suggestions or tell the players what skill to take on the fly - they have to do that thinking for themselves.
It also works for NPCs (friend and foe). The GM can pick a NPC level and profession, allocate how many ranks the NPC would have (although typically I start the NPC with 25% or more ranks allocated to endurance, perception and resistance skills and 25% on their "basic" combat package just so I have an adequate feel for the character). And then select other skills and spells on the fly. The players don't feel cheated because they can do the same thing themselves. Plus, the hour you spent creating a sophisticated, interesting NPC background isn't totally spoiled by the fact you forget to give them Arcane Lore Demons like you intended. More fun, less preparation. This is important when you use Oatmeal for Brains.
Robin