AFAIK, Apple first introduced lightning fast desktop search in Mac OS X Spotlight. Being both a Mac and linux user, Spotlight is one of the tools that I use the most – to search for documents and more importantly, to launch applications without searching for its icon and/or name.
More tools competing against each other is good for consumers. Consumers will surely get choices and developers will always strive for better products. I just hope that antbear does away with Mono. :)