I know this isn't ethical, but is there anything we can do about other sites copying from SU?
Questions & Answers are licensed under Creative Commons Wiki with Attribution Required license.
Since Answer Leaks is respecting all the above conditions, it is abiding by the user contribution license and not doing anything illegal.
As Jeff mentions:
That particular site manages to meet all the attribution requirements for creative commons licensed work from Stack Exchange.
On the page you linked they hit the nail on:
Not only that, but the links aren't
And the bit from the blog post:
Bear in mind that the content on the entire Stack Exchange network is licensed under the Creative Commons Attribution - Share Alike license, so others are allowed to copy and reuse the content as long as they attribute it to the source correctly.
The team have previously defined exactly what they expect of someone reusing the data to do:
Here is the Meta Stack Overflow question that covers attribution issues (what I've said here mostly repeats that). The second answer there can be edited to add in any site you find that is breaking these rules (otherwise, consider emailing the team or posting on meta).