Personally I don't like the idea of some third party having control of major entry points to your website.
Such services can have hidden costs: tracking users who visit your website, introduce advertising, etc. Long urls are a sign of "bad" site layout, as important sections of a site should have a short url already, or even a short url re-direct link controlled by yourself.
The only reasonable use of these services is to hide the ugly urls for personal web pages hosted by ISPs. If you have any control over the DNS (create A record entries like "this_section.bla.com" rather than "www.bla.com/this_section") or use webserver static or even regexp re-direction.
i think that if you have a website receiving decent traffic, you can spend a few bucks a year to get a decent domain name.