They can definitely work; my ex and I was in a LDR for three years, my current girlfriend and I have been 7 and a half months strong.
It can definitely be done.
Traci gave a lot of good advice, I'd like to add from my own experiences.
Webcam and a Microphone- To make the distance easier, most of the time you do things to bring the distance closer, or the illusion that its closer- the most important thing is to be able to see and hear your parter, while you can't touch them, being able to see and hear your partner, instead of being some dis-embodied text helps you feel and maintain that connection.
Trust is good, but I feel the focus on it in LDR is incorrect; just like in any relationship, when they aren't there, you won't know what they are doing. The only difference in local relationships (I use local rather than the common term, "In real life" as distance doesn't make the feelings or the relationship any less real :P ) you possibly have the option of investigating yourself; and in such a case there would be no trust, and quite creepy/stalkerish. If you maintain contact sufficiently, its usually just as clear if something is up online, than if it is in person.
You do have to make more sacrifices than in a regular relationship, time-wise especially. Because you can't bring your partner along to social arrangements, you have to put time aside for them more often; communication frequency is also more important. Whilst not talking to your girlfriend for a few days is okay when its local because you are going to spend the entire weekend with them, in a LDR this can be galling.
Also there are activities you can do with one another, thanks to the glorious internet, which also closes the distance. Watching films together is really good, just find a film and watch it at the same time, being able to share in reactions to the film makes you feel close. Playing an on-line game together in some shape or form helps too, as it is a shared activity which you both take part in, and finally joining some sort of online community (like here
) also helps, or joining in group calls with mutual friends- again, these things help you feel like you share aspects of your lives, like you do in a local relationship, instead of it being this isolated phenomenon which is in no way joined with anything else in your life.
Also, if you want any more information or resources this site, has been of particular help to me
http://www.lovingfromadistance.com/
Long distance can definitely work; especially in this day and age with the advances of technology; and its becoming increasingly more common.
If you truly work at it, and you put the effort love and commitment it can be as rewarding as any relationship.