Just released, you can download it here.
Why use it when Spotlight is built in? It caches versions of your docs locally, so if you ever delete a file by accident, you can still get at it. It also will index your Gmail account if you set it to do that. It also uses Spotlight importers, so that any third party application that provides an importer automatically works with GDS. And unlike the Windows version of Google Desktop, the Mac version does a full text search of the entire document, even large ones.
But for me, the best reason is that I find it significantly faster to return results than Spotlight, although I haven't compared the quality of the results yet. I've switched from using Spotlight as an application launcher to Mac GDS because of the speed difference. Spotlight seems to choke occasionally, taking seconds to respond to the UI and making it hard to see results get filtered in real time as you type.
It took a little over an hour on my iMac to index the disk, but significantly longer on my old laptop with its slower disk and CPU. YMMV.
There's no sidebar, which I really miss from Windows GDS. I prefer the sidebar over Dashboard widgets, since the widgets aren't always visible and require extra key strokes and time to display. With a quick glance, the sidebar can provide all that useful information much faster. Maybe in future versions...
Nice heads-up. It looks pretty cool; nice to hear the performance is faster than spotlight, and it uses Spotlight plugins. I've been a bit frustrated trying to find things in spotlight as well. I guess the only issue I'd have installing this is that it has to have a performance hit to have all these indexers listening to every filesystem change and indexing on the fly. Already on a laptop, I'm concerned about any extra software running. LOL to John's complaint of only indexing the first part of a file on Windows!
Yeah, it would be cool to have the Sidebar (although on XP takes 20% of my cpu when it's not hidden). But if you have the mighty mouse, it's really quick to bring up the Dashboard, especially vs. using the auto-hide Sidebar.
The CPU usage on both my Powerbook (1.5 GHz G4) and Intel iMac are not noticeable, once the one time index is built.
Cool experiment: I edited a text file and put in a phrase that I knew wasn't anywhere on my desktop and saved the file. I immediately did a search for the phrase and it came up, as the only result, instantly. That's fast!
When I had the sidebar going on my AMD 3500 XP machine, it didn't use a noticeable amount of CPU. With iTunes and Firefox idling, the CPU monitor reported around 3% with spikes of 7-10% during a photo transition in the sidebar.
The reason that I don't use Widgets on my laptop isn't the extra keystroke to open them, it's the disk grinding and paging in time required to load them into memory that takes several seconds, which is especially bad on my Powerbook.
I usually just want to quickly glance at something (CPU load, gtalk status, calendar month view, etc) so any kind of hiding of the widgets / sidebar sort of defeats the purpose, in my view.