Stop throwing hardware at the problem !

I've been in more than one situation where I was asked to tune a system where they had thrown a years salary in hardware at the problem already. Only to find out that the app would run just 3% faster or even 10% slower ! I'll bring some examples and will show you what I did and why. This is not just for DBA's, DEV's should also get at least one usefull thing out of this session.