I am perpetually amazed at having to reiterate this, but if you make your site hard to use, then people will not use it.
The current visitor and usage statistics show that people give a site an average of 4 seconds when they come to it before giving up.
Once there they subconsciously think “does this page answer my requirements or allow me to accomplish my task? – if not, is there a link to a page that does? – if not – then leave.”
[sidenote: apparently one of my best skills lies in articulating the thought process that everyone undertakes when they arrive at a site: it’s all down to observation of real users and thinking about how myself use sites!]
So: why then would you consciously make a site harder to use?! – oh, it might be that you are not explicitly trying to do so – but the end result is still the same….
Making links open in new windows annoys visitors to your site… – making the text 10% grey on a white background and thus reducing the contrast on an already hard to read medium annoys visitors… – not answering their questions annoys them… – in fact there are far more ways to annoy your site’s visitors than to just give them what they want.
Put it this way: how many sites do you visit that you take one look at and just think “no” and hit the back button?