While it may be true that some clothing is more effective than others at blocking UV radiation, the vast majority of clothing (unless you like wearing a lot of sheer lace - and hey, what self-respecting tech geek doesn't?) is more than adequate at protecting the wearer. Rule of thumb: If you can't see through it, it will protect you well enough from the sun. Most unwanted/dangerious levels of sun exposure occur on parts of the body that are clothes-free any how (face, arms, ears, etc), so even if these clothes did offer more protection, it would be largely useless anyhow.
Also, a bit of bright, intense sun is good for you (ie, half an hour or less at noon). You just don't want to be out in it for hours (or more than half an hour or so if unprotected). When the sun is at it's brightest - shining most directly at you (at around noon most places) you get the highest concentration of UVB needed for making Vitamin D (optimally at wavelengths between 280 and 320 nm). And you only need less than half an hour of decent daily sun exposure to get more than enough Vitamin D.