Character point debt...hmmm. It can be annoying and it can be a wash, depending on the GM and the player. First, in case you're not familiar with the concept, there is only one mention of it in the Basic Set (p. B295) and that is:
The GM might opt to let you pay for your new abilities by going into “point debt”: any point cost in excess of what you can afford becomes negative unspent points, and until this debt is gone, all future bonus points must go toward paying it off.Some GMs don't use it at all: If you don't got the points, you don't get the pretties. Others use it, but sparingly. Some (like me) use it balls to the wall - but only in certain situations. I think it's a wonderful tool for both GMs and players alike - if used correctly.
Not Using It
This is probably the easiest option. Put simply, if you don't have the points for it...you ain't getting it. This makes sense for many campaigns, and can put a halt to PCs spending a ton of cash to artificially inflate their point totals. It doesn't matter if you're 200 points in debt if you've got teh new awesome cool bio- and cybermods. Who cares about paying back the points when you can just go get new, more, better enhancements.
Using It, With Restrictions
This one is "standard" as far as GURPS goes. If there is some form Transformation available (p. B294), there is probably some form of point debt. The GM could restrict it so only certain forms of transformations actually benefit from this, but that's probably not a good idea, unless he intentionally wants one form of modification to be better than any other.
Using It, No Restrictions
I use this in my own campaigns, because I'm more about characterization than I am about characters. That is, if a character should have a trait I or the players have forgotten, and it comes up in game, the character has it. He'll have to pay for it later with his earned points - but for now, he has it. It makes more sense to me for a doctor to have Pharmacy (Synthetic) than not to have it or to pick it up later. Frankly, it causes dissonance for me if done the latter way. Why wouldn't he have used his skill to figure out what the demon-infected new painkiller did the first time instead of the second time? No, better to be "debt" and playing a plausible character than picking it up later. What does it matter if you pay for it now or later? Some GMs don't like this because it feels like "cheating" (or so I've been told). But my players love it and so do I. I've yet had a complaint about it and in the end, the points are paid back.
When To Use It
Now, I'm not advocating something like "But, oh G.O.D.*, I do not have the super-smiter skill, and it would be really useful for me to have right now. Can I please have it?" "Nay, Munchkin. Thou art an abomination before thine table." I'm talking about situations like "Hmmm, I don't have Swimming...my character grew up in Florida...I should probably have that." Yes, yes you should, O Player of the Forgetful Floridian. It shouldn't be used to amplify a player's power - just fill in obvious gaps. Again, I'm not advocating that you just give the player whatever trait he needs (though sometimes that is a option as well), but to simply let him pay for it later. It's sort of like a "rent-to-own" character trait.
* "Game Operational Director"
Picking Over the Bones
As you can probably tell by my many posts - I am a Rule Zero kind of guy - the GM is not just required to run a game. He's NEEDED. Once you set up a campaign, you need someone to be the arbitrator. Usually the person who made the setting and the person who runs it are the same, but this isn't always the case. There are people who disagree with that philosophy...but they usually end up alone or playing video games. Pity them, for they are sad beings. When it comes down to it, role-playing games are not just a hobby, they're a collaborative act. An act of story-telling between you and your friends. The entire reason there are rules is so that there are guidelines so no one can hit the "I win" button every time - and frankly - that'd be boring. The reason there are dice is, so we can have a little randomness and not be controlled entirely by the rules. And finally, the reason there is a GM is, so he can ignore the dice and the rules so that we have fun. Without these three things working in concert, you tend to get a boring - or at least one-sided game. The GM tells you what your character is going to do and you have no recourse but to agree or argue. Either way...boring. That said, and more on point, it might seem unfair to all other players if the GM gives the forgetful player points to salve holes in his character that do not meet up with his background, but remember, the player still has to pay points for them. And in doing so he is less likely to learn new skills or acquire new traits that are available in play, but not at the start of the campaign. This subtle, but key difference can weed out any abuse of the Point Debt rules before they even happen. If the premise of the campaign is "No one knows any supernatural skills or powers, but can learn them in play" then those who have made sure their characters are what they are supposed to be will have those spare points to acquire said traits in play.