One of the reasons is.gd is fast is because it uses sequential URLs for each request, so it doesn't have to do multiple collision tests. tinyurl used to do this

One of the reasons is.gd is fast is because it uses sequential URLs for each request, so it doesn't have to do multiple collision tests. tinyurl used to do this eons ago, but stopped because of abuses (actually somewhat NSFW): http://en.wikipedia.org/wiki/TinyURL#Early_abuses http://en.wikipedia.org/wiki/TinyURL#Early_abuses