Websites and Web applications are meant to be used only once or few times, so are the perceived usability (correlated to aesthetics) more important than the real usability (time for task completion, number of errors encountered, etc) on the Web?
(I'm not saying that usability is not important, I'm only in doubt if aesthetics is more important to overcome the brutal competition of the Web and the user's attention span than real usability that's not
This is indeed a worthy question, but a proper response requires a book, not a paragraph. If I have to give a short answer, it is the ubiquitous and unsatisfying, "it all depends." So here is a long answer, although still too short to get at the issues properly.
I take issue with the statement that "Websites and Web Applications are mean to be used only once or a few times." That is not my experience, nor do I think this is supported by the data. But that statement doesn't much impact my answer.
First, I strongly believe that for most, everyday applications (products, applications, websites, and web applications), perception is more important than reality. In production environments, such as assembly lines or service bureaus, reality may dominate, but for the rest of us, something that takes longer but that is perceived to be efficient is superior to something that is shorter but perceived differently.
Second, I do not believe that people really make much of a distinction between usability, aesthetics, etc. Basically, they have a holistic view of their experience and only decompose it when forced to. What they care about is: did they get the answer or outcome they required; was it painless; was it enjoyable. Would they do it again (voluntarily, not because they had no choice)?
Quite often good characteristics -- whether usability or aesthetics -- are not perceived, in part because they are taken for granted. The human perceptual and attentional systems are tuned to notice discrepancies and problems, not that which is expected. So we tend to notice things that distract, that impair our ability to get something done, or in the realm of aesthetics, that are particularly distasteful. We do indeed notice especially attractive items(or people), but quite often the attention drawn to the appearance can be detrimental to the task. So the best designs are often the ones that are least noticed.
The fact that good design is often unnoticed does not bode well for our profession: it limits survival value (which in design, means that little attention will be paid to these attributes). Superb usability is only noticed if everything else is so bad that the improvement increases user satisfaction and sales. Appearance is similar: if the new appearance is sufficiently good to be remarked upon, then it might enhance sales. But without compeling evidence thatthese design factors matter, marketing forces will push toward things that appear to give competitive edge, which in most instances means lower price and extra features. This trend continues until the point where the "enhancements" get in the way, and then suddenly the cry will arise for better usability ("can't we make it simpler!") and better design ("hire someone to make itlook pretty." You shouldn't like this answer, but it what we have to learn to live with, ecept in the most sophisticatedof comapnies. This attitude differs for prestige items (see my discussion on reflective design below), but websites seldom fit into this category.
If the question is, how much attention should be place on usability, aesthetics, and pleasurable interaction for different classes of products, then the above reasoning leads to the following "it depends" answers.
For truly one time uses (for example, to answer questions such as "what time is it right now in Rio de Janeiro?") I suspect ease of getting the answer dominates all else.
For repeated uses, such as my own personal use of my.yahoo for keeping up with news headlines, weather, and the stock market, aesthetics matters slightly, rapidity of scanning the information matters a lot, and my ability to tailor the selection and placement of just the information I care about dominates. For Google, functionality coupled with the clean, elegance of the interaction dominate. For shopping sites such as Amazon.com or Netflix.com, the ability to look up things rapidly, get authoritative information about them and high-quality reviews, coupled with ease of ordering dominates. These sites are not aesthetically exciting, but the aesthetics do not distract. (Amazon, though, as it expands to cover all things sellable, is in severe danger of losing these virtues).
For products that are on display in my home, whether or not they are frequently or seldom used, aesthetics often dominates.
Now I come to prestige items, where reflective design dominates. For such major display items as clothing, jewelry, watches, cellphones, and automobiles, aesthetics and functionality matter, but here the reflective side of design plays a critical role: the choices of al these items says something about the person, and so here fashion, brand image, and other reflective characteristics can play more important roles than function or aesthetics. Usability? That barely matters, assuming that it is at least at an acceptable level. On the whole, I have found that usability is always secondary or even tertiary in people's judgments about products. As long as it is "good enough," most people don't really care. More to the point, they seldom base their purchase decisions on this dimension. The lack of attention that industry pays to this dimension is, therefore, often quite reasonable.
A personal note is relevant here: I am an exception to this rule, but only because my public persona is that of a usability expert, so I have learned that other people scrutinize every object I own, so I have to justify my choices -- but once again, even though the dimension may be usability, it is a reflective side of being usable. Now that I have championed beauty and pleasure, the range of scrutiny of my objects has expanded, but fortunately, I now have more room to explore and enjoy objects, rather than simply aim at usable ones.