Slewis how much larger do they make the device?

I used to have a crystal case for my N95 and kept it on for about a year. I found that after taking it off grit had got in underneath and had been rubbing against the body causing excess wear. I also found that when taking it off the phone was noticeable thinner - the case added more to the volume than I first realised. I thus made a decision never to use these type of cases again - but might reconsider for the N900.

I see people with iPhones (a real masterpiece of engineering; not that the N900 isn't good), and they buy £2 cases from ebay that almost double the size of the device... Don't these people know how many thousands of hours designers and engineers worked getting these things so small and then you slip on a cheap piece of knock off crap from china!?