So it was established that the best way to handle experience in the open gaming table is to just start everybody off at 0 and go from there, it sorts itself out.
But, I fool that I am, thought to myself, "But this kind of makes players unable to play characters with level adjustments or racial hit dice." Sure, there are various monster class progressions (and if you want to play a character that doesn't have a published monster class progression, I can just make one). But what of +1LA or +2LA? It would be awfully silly to make a one-level 0HD class progression, I'm not even sure how it would work (start with a racial hit die and then once you've completed the monster class progression you can switch it out for a class level? Inelegant).
And it's not great to just say you can start at 0XP with +1 or +2LA, because then you're stronger than the other characters for free and there's no reason not to do that, unless you don't want to deal with LA later on.
So I decided on this compromise: if you've got a character to level n, you may make a new character at 0XP but at level n, as long as n-1 of those levels are racial hit dice or level adjustment.
Sounds reasonable, right? Nope! Of the two players who have decided to take advantage of this offer so far, neither got it right. One missed the second part and made a character with two class levels (which I provisionally allowed because they were cleric and barbarian, so the character wasn't really actually much stronger than a level 1 character). The other made a character with a monster class level and a regular class level (which I'm allowing, as long as your monster levels are equal to or greater than your class levels, until you finish the monster progression), but didn't actually have a level 2 character in the first place (which I allowed, but the character conveniently died and was resurrected in the first session in which he was played). This is, uh, not auspicious. I'm going to call this policy a failed experiment and do away with it.
What to replace it with? Maybe nothing. Or maybe I'll do what Vaxia did (with pretty much great success) and say that, if you choose to permanently retire a character (e.g., if the character dies, or you grow so bored of them you know you'll never play them again) you can transfer 75% of their experience to a brand-new character. (In Vaxia, you could also transfer the experience to an existing character, but only in the form of banked XP that you had to work off through RP in order to earn. D&D doesn't really have a mechanic like that, so I'd just say brand-new characters only.)