It would be nice if it can also warn users that a given combination is incompatible. E.g. the Apache License version 2 and the GPL version 1/2 are not compatible. The current comparison suggests that they are.

This site was discussed 3 months ago: http://news.ycombinator.com/item?id=4193152

This "combine" feature seems new though.

I don't understand how it works. I tried MPL 2.0 and GPL 2.0 and it doesn't say that they are incompatible, in fact it seems to say that the licenses can be used together.

http://www.gnu.org/licenses/license-list.html#MPL-2.0

So basically it has the same problems already discussed 3 months ago.

TL;DR: don't trust the site.

EDIT: formatting