For some reason, time values (usually displayed on the horizontal axis) are reported in only one or two digit accuracy, while data plotted on the vertical axis can have four or even five digits. Folks with poor eyesight might have trouble extracting data from the plots.
General Comments on Usability: Problem 9.5.10 has a lot of potential, but setting the animation for a resonance condition using the accompanying plot is tedious. The slider in problem 9.5.1 does not return to zero when reinitialized (as it does in problem 9.5.3). Problem 9.5.5 has a plot that suffers from 2 digit time readout. Right clicking the plot spawns another plot that has even less precision in the time readout. Several of the problems have a slider to control the independent variable, and display a value rounded to the nearest integer. If this value is used (rather than a more accurate one that can be obtained another way) the calculated results can be far from the given answer, causing students to doubt their methods. Several of the problems have "Start" or "Close Switch" links that are superfluous since the graphing is automatically performed when the applet starts, and the pedagogical value of seeing the graph redrawn is nil. The horizontal and vertical scales are confusing because they often have a factor (e.g., 103) which is well-separated (and easily overlooked) from the labels on the axes.
Physlets are customizable and may be hosted locally. The problems in this collection should be considered as a starting point for a new set of problems modified to address any perceived shortcoming. A guide for scripting Physlets is the text Physlets: Teaching Physics with Interactive Curricular Material by Christian and Belloni.