The scalometer:

The principal advantage of rating scales is that they are simple to use and require little effort from the respondent. However, there is a tendency for respondents to avoid choosing extreme categories, but instead to select a position in the middle (known as "central tendency"). This can be overcome to some extent by ensuring that an exact middle point is not offered, thereby forcing respondents to indicate an opinion one way or the other. However this may influence the reliability or validity of results. Respondents may also offer what they consider to be "socially desirable" responses, rather than expressing their real views.

The success of a survey is also heavily dependent on respondents accurately indicating the strength of their views on the scales given. These shortcomings are less important if you are studying a simple topic, but if you are dealing with complex or emotional subjects, a more sophisticated approach, using multi-dimensional scales, is necessary.