Because it is the easiest I normally use google converter for converting btc to $. In case you don't know it's pretty easy just type 0.25 btc in usd and google converts it for you. Normally I just convert the amount I currently have in my wallet to see if there is enough in it to buy something.
So last time I did this I noticed something, Google also does a normal web search if you type this in. And Google found my address because I typed in all the decimals and it seems that there were just 1 address with the exact same balance. So any btc converter could just assume that if there is a really accurate number, that you are the owner of a the bitcoin address with this balance. If you are logged in your Google account they even know your name and everything.
I know this is same pretty paranoid thinking and I guess LE could never use this, but I don't want Google or anybody else to know how many bitcoins I have and where they are.
I think preev works pretty good