I think that one of the best aspects of the GURPS RPG is the Disadvantages and Quirks. Other role playing games will try to encourage you to make an "interesting" character and "develop a unique role" and then proceed to provide absolutely no incentive for doing so. Other RPGs will present player races that have numerous difficulties (like playing a Jawa or an Ewok in a Star Wars setting) and then provide absolutely no additional benefits for playing these difficult characters. The Powers That Be at SJ Games who designed GURPS made a very wise design descision: Pay the players to make an interesting character. Smart.
What follows is some advice on what disadvantages you should choose for your character that you will realistically be able to role-play, that will help get a character into adventures, and that will keep things fun and interesting.
Credit Where It's Due: Lots of the stuff on this page comes from Jared Whitley. The original document that was essentially cut-n-pastes of his emails is still available here. This document is a re-write of the original (better organization, etc.).
Before we launch into the specifics, here's some generic advice that applies to any kind of disadvantages you might take.
Some characters have trouble coming up with a well-formed list of disadvantages (i.e. ones that fit their character, harmonize well together, etc.) or have trouble filling up all their disadvantage slots. The following listing of disadvantage categories can help you accomplish all of those goals. The alert reader will note that this list bears some similarities to the Character Creation Checklist page.
These are disadvantage that confer no actual game penalties (i.e. no minuses to anything), but you are expected to roleplay your character in a particular way to comply with them (if you fail to roleplay these properly, the GM will dock you points). These can actually be some of the best kind of disadvantages to take.
These are disadvantages that explain why your character goes adventuring. Everybody should take at least one of these for two reasons: 1) It's a great hook for GMs to use and 2) you're going to go adventuring anyway, so you may as well get points for it. Jared has already written up a whole page of motivations so rather than duplicate all the information here, I'll just direct you to that page.
Some of the most obvious motivational disadvantages are:
This category of disadvantage explains why you have a loyalty to your teammates. I've already written up a whole page on this, so I'm not going to duplicate it here.
I will sum up the above page by saying that there's a 5 point disadvantage everyone should consider taking: Sense of Duty - Teammates.
These are disadvantages that incur a few negative reaction modifiers or cut into skills your character wouldn't get anyway. Most of these only give you about 5 - 10 points. This is usually as far as most players go severity-wise.
This category includes any disadvantage that has a serious deliterious effect on your character, especially in athletic / combat situations. In fact, this entire category can be summed up in two words: Physical Disadvantages. No sane person would start out with any of these. In fact, I think the only reason why they exist is to provide a detailed description of what happens to you if you roll something bad on the critical hit table.
In truth, there are some major disadvantages other than physical that you would never want to take at generation. Some examples are:
These will cause problems but be a lot of fun. Everybody should get one of these, or at least consider getting one.