Even when I first installed it (around 2005), LookOut was already sold to Microsoft. They planned to integrate their search tech into Windows and Office. And did they need it.
Anyone who has ever had to try and find anything filed away in a reasonably large Oytlook pst (say, over 700mb), would relate to frustration and pain. Outlook search is dumb. Most people I know end up doing searching by sorting — by from, to, date or subject — then trying to browse the result for that very email.
LookOut only needed to index your PSTs (and any document folders too) once, then keep that index up as new items were added. First run could take a couple-three hours, but it was worth every minute. Just take a longish lunch and a staff meeting, then you're done.
Outlook 2003 came out without any search improvements (unless one wants to consider search folders anything like a "search improvement"), but 2007 version did gain Windows Desktop Search. That was where that purchased tech must have been applied. But was it a good application?
No. It took me several DAYS to get my PSTs indexed. And even after that it is nowhere instant. Interface of Outlook Instant Search is clumsy — it gets in a way by trying to both search and redraw the UI. Explorer-based UI is no better, although I find it at least less interfering, yet distracting nonetheless.
Microsoft should really look at how this was done before, or how Google, Copernic or, gasp, Apple do this. And simply NOT "improve" it.