When Apple introduced Spotlight, the powerful search technology which is part of Mac OS X 10.4, Tiger, this was the first real-world application of instant searches of files, their content and their metadata. It was also the first consumer application of real-time searches of this data; except that, on most Macs, it wasn’t quite real-time. Many users lamented the time it took to run Spotlight searches, and it’s true that on slower Macs, the time necessary is excessive. On my previous Mac, an iMac G5, some searches would take several seconds, and searches that resulted in thousands of hits (kind:music, for example) could take a couple dozen seconds.
Some of my colleagues have railed against not only Spotlight but the lack of simple Finder searches, such as were available in previous versions of Mac OS X. You can no longer simply “find files” from the Finder; you have to use the Finder search bar, which is simply a different interface for Spotlight. The complaints are the same: this can be very, very slow.