I don't think the problem with substring searches is speed. I think the problem is the way the searches work, since they are fuzzy-searches on each letter triplet, that you would need to type too many letters to complete your search. The goal of the search interface was to reduce the number of keystrokes, not increase them.
Then again, I ran into a situation recently where a substring search would have come in handy. I'd downloaded a song from the Blizzard Software people, called "Greetings - Deckard Cain Rap". It's a gag song done with the actor who played the part of Deckard Cain in Diablo 2. If you've played Diablo 2, the song is quite funny.
Anyway, I knew it was "Deckard Cain Rap", but I didn't remember the "Greetings" part when I wanted to play it for another Diablo 2 fan. I kept typing in "D-E-C-K" and it would say "no matches". I got frustrated because I
knew it was in there.
So, at that point, a substring search would have helped me. The only question is... how many more keys would I have needed to type to get the song to appear? Is there a way to figure that out statistically?
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Tony Fabris