The effects are nothing like those of heroin. I should know, as I've used both in the past. It is addictive however, and I would advise anyone that takes xanax daily to switch to a longer acting benzo like klonopin or ativan.
I was prescribed xanax starting at .5mg 3 times per day, and over the next few years I became extremely addicted. As my tolerance increased, my dose increased to 2mg 3x per day over 2-3 years time. I reached a point where I would wake up sweating, having withdrawal symptoms, craving my morning dose of doctor prescribed xanax. I asked my doctor to try another benzo, and she prescribed me klonopin. I take the same dose, 2mg 3x daily, but I've never experienced any withdrawal symptoms, even after missing as much as an entire day of klonopin. I get the same benefit for my panic disorder with klonopin, but I don't have to deal with the awful side effects that xanax gave me at the same high dosage. Save yourself the trouble and stay away from xanax, the devil's benzo.
Peace