Good question, Ropera. There was a thread on AdAware's forum about this shortly after the refupdate that detected Alexa came out...it's probably still there.
As I understand it, Alexa is more than a single product. The element that is integral to IE 5.5 and above enables the "Show Related" link found under the "Tools" button. I chose to remove mine (after backing it up) since I do not use this function. I personally, do not believe this particular element of Alexa is capable of transmitting any information however, that's just my opinion. I removed it to "err on the side of caution".
BTW, running the IE repair tool will reinstall the Alexa .reg entry.
I did the same thing,Adaware says it's spyware so I removed it.I don't use that option either,and no problem so far.As was mentioned if you ever want or need it,just run the IE repair tool or use the backup,Tuff