Ruby's symbols are often talked about in terms of efficiency - taking up less memory and executing faster. While these are both laudable goals, symbols are more than just performance improvers. The ability to name things is valuable semantically. Take a look thru p&p's Composite UI AppBlock and you'll see strings used as names for things all over the place. It's great for loose coupling, you see. But how do you tell the difference between a string used as a name and a string used for some other reason like user input? You can't.
Rails makes extensive use of symbols - anyone who has Rolled on Rails has seen "scaffold :recipe". That's just the tip of the iceberg. Rails uses symbols extensively across both ActionPack and ActiveRecord (and probably others I'm not familiar with). It's a great approach, but one that's unique to Ruby as far as I'm aware.