Before, I realized I could do this, I rarely ended up using the lens hood on my digital SLR.
But while I was walking around, I saw a professional photographer who had his hood mounted in reverse on the lens.
I tried it and it worked. Now I can carry the hood with me all the time and use it more often than I used to previously.
More info on lens hoods:
and this interesting discussion on Flickr - http://www.flickr.com/groups/tamron17-50mm/discuss/72157604024209303/