My qualm with this app is for a Linux user you can already build a system like that to yourself by simply using telnet and typing the HTTP directly down the pipe. The bonus is that you get to memorize all the protocol messages that way too.
Hurl is not enough for some of the tests I want to write, i.e. testing sending a 50MB file, or dynamic content.
If you're going to do a single request or a few requests in isolation, curl is the way to do.
If you wanna do a full fledged testing suite, might as well using a proper scripting language or a test framework.
Hurl hits the spot between those two for me.