I can see two reasons why I wouldn't use it in preference to Google:
- there's no autocomplete/autosearch on search terms
- more fundamentally, the results are less easy to read because they're in columns. The duplication of information detracts rather than adds, and for both Bing and Yahoo the boxes have horizontal scrolls as well.
So for a basic search engine I think it's less usable because of the multiple results.
I can see this is helpful if you're trying to compare different search engines, but I would have thought this is an infrequent need for most.
For what it does, it works very well, mind.