If you're having a problem you want to report...
Some common issues and possible workarounds are described below.
When interacting with the crop widget, the window jumps to upper left corner of cropped image. This is generally a feature until you're trying to move the crop selection around an image that is larger than your current window.
This issue is related to keyboard support. If you set option keySupport: false the jumping will not happen. Nor will keyboard support work. Alternatively, read the section about handling larger images.
There have been a couple of odd reports about numbers being strings. If you are having a problem where a number seems to evaluate oddly (e.g. 25 > 140) it may be a string. Please change any instances to e.g. parseInt(var) to test.
I am not aware of any reason that would happen, so it may have been in client code for the cases reported. Anyway, if you're doing arithmatic with numbers and things are going strange (or if Jcrop behaves strangely based on setting values with the API), make sure you're using numbers by casting them specifically.
If you find a case where you think Jcrop is causing the problem, please let me know.
When Firebug is enabled, it causes slight performance issues. Jcrop is by no means unusable, but if you disable Firebug you will see a performance gain, even if you're not using it to actively profile anything.