[charleski]

Actually, if you want this to work properly in iBooks you need to add something else. ADE-based readers will split on a soft hyphen and hide the hyphen, whereas iBooks splits and shows it (which is generally the desired behaviour, but not here).

Add the following to your css:
span.hide { visibility: hidden }

then place the following at the points where you want long urls to wrap to the next line:
<span class="hide">& shy;</span>
(again, remove the space between the '&' and the 'shy').