Instability issues aside, there are a few things I like and dislike about it.

Likes:
It’s more robust if you want to do things outside of your desktop. Searching for anything in your browser is relatively fewer keystrokes away than Quicksilver (unless you set up some custom triggers).

Dislike:
For just accessing items within your own desktop, it doesn’t do it quite as well. It always mixes in Google searches in the results. For example, if I typed Adium in Quicksilver, it will always search through my desktop for relevance first. With Google Quick Search Box, inevitably there’s an option to search Adium on Google’s website. Eventually Adium will rise and become the #1 result, but I wish there was a prioritization system where web searches is the least prioritized by default.

Since it also searches from Spotlight (and most of the time you *have* to, because the first time you search for any result it may not familiar with, you will have to go through the Spotlight results for the correct ones), the performance for even mundane tasks can sometime be sluggish compared to Quicksilver.

Granted, “sluggish” means a few extra seconds, but on an older model Mac it would take a lot more time (my co-workers 12″ PowerBook had a really rough time). Quicksilver was extremely fast & robust because it maintained its own index. Using Spotlight does give you more detailed results if you’re looking for some very obscure file, but even when you’re just typing in the name of an application in your “Applications” folder, Spotlight will slow down the responsiveness of Google Quick Search Box.

The advantage of being able to quickly get web search result is a bit offset by Quicksilver’s web search plugin, which can get you more than a dozen different search engine with a few extra keystrokes.

For now, I’m sticking with Quicksilver.

A lot of people never use QS because it’s complicated and has a bit of a learning curve. Maybe this tool from Google is a better fit for them.

Second, Google’s QSB is extremely new and cannot be even compared with Quicksilver (reason why I left that disclaimer). Besides the app itself being developed the community needs to create those awesome plugins. Only then will it be really usable. Besides, even UI-wise QS is more powerful (Quicksilver has the three pane UI against QSB’s two pane search-list UI). Maybe Google’s QSB will become the newbie’s Quicksilver? Who knows.

And aside from that, you’re really comparing apples to oranges. Search is only one thing QS does. Add in image manipulation, ftp uploads and clipboard access are just a few features that make QS much more than just a desktop/web search tool.