From both ends – the Internet Marketer, and as a user of the web – URL Shorteners like goo.gl and bit.ly should carry a mental warning label “Use With Caution.”
As a user, you should be aware that a URL shortener can hide a link to what would otherwise be obviously a spammy or dangerous site to visit. So click with caution, have your anti-virus software up-to-date, and be prepared to hit your back button.
For the same reason, these URL shortened links are increasingly being blocked. Meaning if you have such a link on a web page, or in an email, it may not be a functional link at the other end.
The thing is, there is no good reason to use a URL shortener except where characters are at a real premium.
And that means on Twitter, where they are indeed useful.
Otherwise, they may be cute, but pointless at best.