Not necessarily - pissed-off yet addicted users are often the driving force behind adoption of competitors, should one arise. For example, Y!Mail adopted its redesign about a year after GMail came out, and a lot of my friends that had been loyal Y!Mail users (and GMail holdouts) switched because Yahoo was taking away their UI anyway. Most of the modern Harry Potter fandom sites (FictionAlley, SugarQuill, GryffindorTower) were created because Fanfiction.net abolished their forums. The final nail in classic Netscape's coffin may've been that they changed their UI for Netscape 6, so that IE5.5 was more like classic Netscape than the new Netscape was.
The difference is: name a web site that could POSSIBLY work as a replacement to Facebook.
New Facebook is still fast. It's incredibly effective. It's just new, and as such takes some getting used to. Once the change is done, people will adapt. And the reason they will? Because no other web site has TRIED making a platform as powerful as Facebook's. Not even Bebo or Virb come close.
