The complaints I most often hear about things like training time and fees is that it's additional bookkeeping and that it penalizes the character by A) costing him hard-looted cash, and B) means he doesn't get to "level up" mid-adventure. Of the two, I more sympathetic to the latter. In some adventures, you might be stuck far from civilization and/or unable to take time off from a quest to train. This means the character (and the player) have done the work, put in the time, made the effort, etc. and are being denied their "reward." They've accrued the X,000 more experience and want their new spells, dammit! This can be felt even more acutely when a "storyline" is building toward some sort of final confrontation, and the player wants his PC to be at full capacity when the caca hits the fan.
Feeling kind of invincible, really.
In order to level, PCs must train and study. The cost of training is 1000gp x the new level and takes a week. During that time, characters are doing nothing significant except training (8-10 hours/day+). Clerics fast and pray, rededicating themselves to their faith. Thieves pay guild fees and refine techniques for things like picking locks. Magic-users pay their guild to learn and copy new spells. Fighters work out, practice, and attend vigorous sparring sessions to refine their techniques.
Now, what about the "stuck in the wilderness/hot pursuit" scenarios? Well, here's what I propose. A character that reaches a new level but is not able to formally train still sees some benefit from their accomplishments. Namely, they still gain their new HD and saving throws. (I would give spell casters more spells per day, but that gives the advantage to clerics over MUs, as they don't have to copy new spells to learn more.) Other benefits like improved attacks, skills, new spell slots/levels, etc. have to wait until training occurs.
So, what if –for some reason– the PCs simply cannot get to a place where they can train for an indefinite period? Well, then the PC can train on their own. How does this work? The PC practices/prays/studies on their own for a week, or for 1d3 weeks if they are doing other things like traveling or adventuring while training. At the end of the time frame, the PC makes an ability check on their prime requisite (classes with more than one prime use the higher score). A success means they have successfully self-trained. A failure means they cannot improve without formal instruction. A PC cannot self-train more than once without having formal training to level up the next time.
Now, this is by no means the only way to handle this. What I'm after here is a specific kind of game. One where the PCs are routinely in places like cities and towns, giving them plenty of opportunities to hear gossip and current events, meet NPCs, gather rumors of new adventures, re-equip, hire retainers, and so forth.
To be fair to the players, such a system certainly wouldn't have things like reduced treasure awards. A typical adventure would have the potential for earning/finding a reasonable bit of change. I could see a megadungeon-based game working well with this system; where player characters frequently return to a "base" after an excursion. In a more open game, where the PCs move about, I would want things like the guilds and training halls to be fairly ubiquitous, so the characters could find one without having to travel halfway around the world. Any good-sized town or city would have these sorts of resources. Is that super-"realistic"? Probably not, but if I'm going to bilk the PCs out of thousands of gold pieces, I'm not going to give them grief by making it hard for them to spend it.
What have other people done about this idea? What are you experiences with training costs, etc. as a GM or a player?