I'm not the author, but I too had problems with it in old days. First versions of Spotlight were very buggy and sometimes the background indexer slowed down the computer very noticeably (eating up 25% and more of processor time). Apparently, it had something to do with the first invocation: if it didn't manage to index all at the first time (which could easily happen if the user restarted the computer), then it entered that processor-hungry mode.

Another thing is bad UI. It starts to search as soon as I type it, which, for me works so: I type one or two characters, then it freezes because it starts searching and finds everything with these characters. Then after a few very long seconds it thaws out and I get a chance to type the rest of it and also set search options. I almost always search for file name, not contents, so I have to set this option on every search.

Somehow I don't have these problems on Windows; here I always have a chance to type the whole phrase. I also use content search much more often, that is, I don't bother setting options, I'm content with the results :) (My PC hardware is faster, but not that much faster; I think the problem is in bad timing.)