Lifehacker (one of my favorite sites) loves Quicksilver, but I could never figure out how to use it in a way that made it more useful than Spotlight. Using an app launcher is always faster than using the dock or browsing Launchpad, but I've never been able to do more than that with Quicksilver.

I used QS for a bit, but I found it lost items if you hadn't used them in awhile and never found newly loaded apps, making it rather pointless. Spotlight is fast and finds all my apps and files just fine. Spotlight categorizes items nicely, like todos, contacts, docs, apps, etc and is just as quick to bring up as QuickSilver using CMD+SPACE, plus it's already in the OS! No updates, no plug-ins, no config, it just works. Honestly, Spotlight is one of many amazing features of OS X that got me to move away from Linux.

I tried Quicksilver out a few times, and maybe I am just not worthy enough to understand and use it. It did not come natural to me, but I tried to get around that. I think I still need to watch some screencasts. The smartest man at my company uses this like no other (yet he claims he hardly touches it), and does some amazing control with it, like searching through our python source code, launching apps and having them do something he wants, contextual web searches in our in-house webapps.

Like I said though, I could hardly understand the preferences and setup of it. Then, once I started pressing the hot keys I had no idea what to do or what to type to get it to do what I might want...like some of those examples above. I think there is so much you can do with it, so many possibilities, that it can be overwhelming for a new user.

I also had a bad experience with its Triggers functionality. This allows hotkeys to do actions. I wanted it to simply paste in some text. I had to go to forums, set it up, didnt work, read further into forums, some people have certain exentions, others dont. I got it to work...and then a few days into it all, the trigger acts up and instead of pasting text, some how controls my browser to go to another page and enter the text there. Ooops.

In the end, I think its kind of like linux. I am sure it can do tons and once its setup you are golden. I still want to figure it out, the effort to do it is no simple task.

Mac essential, definitely. Not sure whether I prefer this or Gnome Do, but with them both being available only on their respective platforms at the moment, it's not much of a contest.

I think Quicksilver is one of the apps that makes me stick with my Mac. It's that good.
In the past it has had loads of stability issues and I had to uninstall it for a while - it broke my heart. But I'm glad to say that since installing the latest build (B56a7) on my Snow Leopard machine it has not crashed once (I've had it installed for about a month now and I've used it every day).
I really love this app and it's the first thing I tell anyone new to Mac to download, use and love.

I'd like to shake Alc0r by the flipper, but I fear I am not worthy.