This is something where I think Catalook lets itself down. It looks like it's not easy to setup, but from my own experience the doc just covered all possibly issues people might have with various changes to a standard setup - making it look complicated and a bigger challenge than it really is.
Documentation is mostly thorough but various things are not completely well written and the skinning really could do with a rethink, I think. Or maybe at least much clearer documentation for it. It is very customisable though I would say... and there's other tools such as OpenWebStudio or XModPro that would allow you to easily build add-ons for it.
Overall it's quite reasonable to use, is very functional and featured pack for a store though not actually multi-currency which was quite a disappointment for me and led me to using a separate Portal for each country/currency. It does a rough conversion of currencies so others can be displayed, but it's only an estimation and payment can actually only be made in a single currency.
The single most impressive site I've seen recently with Catalook is - http://www.sakesocial.com. Another site worth a look is http://www.catalooksupport.com.
Overall it's not bad, a few bugs and incoveniences I'd like to see sorted (and have asked)... usually these are sorted fairly quickly, especially if significant.
I think these quotes from unknown sources are really to plug other things.