Please, it's not my intention to set off a religious war. I am currently evaluating XOOPS and PostNuke and would love to hear from people on why they chose XOOPS over PostNuke or vice-versa.

Look here
And here
Possibly here, too
Perhaps this one is good

I just searched for "Xoops phpnuke" in the forums and got a load of posts, so check them out - some might be a bit old, sorry.

What annoys me a little about PN is that to me it seems a little more complicated for no reason. For example: the permissions and groups areas in PN, it takes a lot more brainwork to set those up then it does for XOOPS but the end result is the same. Its the same thing for Banners as well, i had a heap of trouble trying to get a banner to show in PN. I found that there was so many little things that annoyed me about PN, like having to install auto theme and the compatibilty pack before you could use most themes.
PN has a lot bigger community and this means there is a lot more modules and themes etc to download, but what I found is its still hard to find what your looking for anyway.
I like XOOPS so I am biased, but I really think that XOOPS is already great even though its younger and smaller.. and will only get better.
Another thing about PN is because it is more complicated you need to make more trips to the forums to find answers to your problems and just from my personal experience, even though there is like 200,000 posts there, I would take hours searching and sifting to find answers to the most basic things... this is very annoying!

On a sidenote, I think E107 is another great CMS and if I wasnt using XOOPS i would likely use it.

What annoys me a little about PN is that to me it seems a little more complicated for no reason. For example: the permissions and groups areas in PN, it takes a lot more brainwork to set those up then it does for XOOPS but the end result is the same. Its the same thing for Banners as well, i had a heap of trouble trying to get a banner to show in PN. I found that there was so many little things that annoyed me about PN, like having to install auto theme and the compatibilty pack before you could use most themes.
PN has a lot bigger community and this means there is a lot more modules and themes etc to download, but what I found is its still hard to find what your looking for anyway.
I like XOOPS so I am biased, but I really think that XOOPS is already great even though its younger and smaller.. and will only get better.
Another thing about PN is because it is more complicated you need to make more trips to the forums to find answers to your problems and just from my personal experience, even though there is like 200,000 posts there, I would take hours searching and sifting to find answers to the most basic things... this is very annoying!

On a sidenote, I think E107 is another great CMS and if I wasnt using XOOPS i would likely use it.

I have to agree with Seven on a lot of the issues with PostNuke - I have used both and decided to stick with Xoops.

PostNuke also seems to be distributed with many superfluous modules, an abundance of stuff you'll never be likely to use. And whereas the XOOPS community seem to develop practical applications, the PN community creates a lot of modules that are either duplicates of one another, or of very limited practical use.

I've not tried E107 to be honest - there was something about it that didn't appeal to me, though I'd already found XOOPS so I probably didn't give it the time it deserved.