There are examples of advanced functionality performing well enough. Google Docs is quite fast, especially for what it is. On the other hand, there are sites w

There are examples of advanced functionality performing well enough. Google Docs is quite fast, especially for what it is. On the other hand, there are sites which are conceptually much simpler but incredibly sluggish. Twitter is a particularly bad offender after you've scrolled down a few pages. Or any other site that uses a ton of Ajax with little regard for the consequences.