Lacking luck is one thing (like accidentally buying a case that won't take all of the components that you selected properly) but sometimes there are some motherboard designs that clearly don't make sense. One such example has been found recently in the MSI K8N SLI boards.
MSI messed up one of its premium motherboards as you won't be able to fit a Geforce 7800 GTX in it. It's an SLI system and people at some forums discovered that one of the capacitors will interfere with one of the cards.
There seems to be no escaping the sad fact that one of the capacitors on this board seems to be in the way, making proper fitting impossible. So, no SLI G70, Geforce 7800 GTX for this MSI board at the moment. Seemingly a revision is on the way.