The results are depicted in Figure 7 . Fitting CDF on entire data set by minimizing the sum of squared residuals. These results raise the immediate question as to why the time costs are so low. A time cost of 1 cent a minute is only 60 cents an hour. Several hypotheses suggest themselves.
Users are non-representative.
This is likely part of the story. Our users are volunteers, many are students, and it is apparent from Figure 4 that certain occupations have much higher time values. The only way to deal with this is to try to repeat the study with a different sample, which we hope to do. Other uses of time. Indeed, we have already mentioned that users tend to leave 8 Kbs service on all the time so that email could be downloaded in the background.