I guess any answer to your question will also depend on your field of study. 

In my field -- economics -- there has traditionally been a huge difference in the perceived quality and status of a U.S. or Canadian Ph.D. degree in economics on the one hand and a (continental) European doctoral degree in economics on the other. (Aside: what matters is the thoroughness and breadth of learning and the research skills that comes with the pursuit of a degree, *not* the nationality of the degree holder.) 

 - A Ph.D. degree from a high-quality North American graduate program was (and largely still is) seen as *the* vehicle that opens doors toward obtain an assistant professorship; in contrast, most (all?) US universities would *never* bother considering applications from persons who had just received a doctorate in economics from a European university. Conversely, universities in the German-speaking European countries (i.e., including Austria and Switzerland; sorry, I'm not familiar with the situation in Poland) will pretty much automatically waive the requirement of an habilitation for job applicants with a North American Ph.D. degree in hand for professorships. (Aside: If they didn't waive this requirement, they would simply exclude themselves from the most important segment of the job market...)

 - Most American academic economists have never heard of -- or are at most barely familiar with -- the concept of a "habilitation". To the extent that they think they know what it is, it's widely regarded as an awkward and embarrassing device by which a person enters an extended period of indentured servitude to some "big name" professor, during which time the "habilitand" should develop and demonstrate serious research skills and, ideally, manage to publish a couple of well-regarded papers in top-notch journals. In fact, to the extent that the habilitation degree has any value at all at US universities, it's the publications that (should) go along with the additional academic degree that matter, but not the degree itself.

 - If you're about to graduate from, say, a German university with a doctorate in economics and wish to pursue an academic career, you may be contemplating whether to (a) stay in Germany and "habilitate yourself" at a German university or (b) move to the U.S. and pursue a (say) two-year post-doc program at a leading academic place. Judging by the choices made by people in similar positions in the past, I think it's fair to say that option (b) is the first choice for many a serious budding researcher.

 - I mentioned earlier that the quality of a (continental) European doctoral degree in economics simply doesn't measure up to a U.S. or Canadian Ph.D. degree. (To make the comparison fair and relevant, let's focus on just the few dozen top degree-granting programs in both continents.) This difference in ranking has begun to erode a bit in the past couple of decades -- but only for those European universities that have switched their approach to graduate education to mimic the U.S. model. The economics departments at these universities have, incidentally, also by and large abolished granting "habilitations". After all, the doctoral degrees they award are really meant to be the equivalent of (or, hopefully, far better than) the traditional doctorate/habilitation combo.