I haven't heard of lacona until you just mentioned it, but it does look nice. They also have plugins written in node, but offer a more "natural language" search, which Zazu doesn't. Zazu is also completely open source, but they have a paid version. Zazu is all cross platform, but Lacona only offers mac builds.
Zazu does allow for keyboard shortcuts, and can do everything the Alfred workflows can, but does not currently provide a GUI for creating the workflows. The biggest difference for the plugins, is that they are written in Node so they can be cross platform.
I haven't installed Quick Silver in many years, so my understanding may be dated, but at the time it didn't offer many intuitive actions, such as copying the calculator result to your clipboard.
Alfred doesn't treat plugins as first class citizens, only alfred can have the top level search space, all plugins have prefixes. Plugins in Zazu are first class citizens, there is no built in behavior so you have more flexibility with what you want.
Zazu is also cross platform, so switching between Mac and Ubuntu for instance wouldn't hurt your workflow. Alfred and QuickSilver are Mac specific.
Yes, since the first file finder needed to be cross platform I create a cache in the plugin, but a mac specific one would be great! :D
Technically it spins up another process and recursively goes through a whitelisted set of directories. It caches just the app locations, not all the files.
I just installed on a fresh install of Ubuntu, but maybe this is debian specific. It looks like I just need to add my email address to the author field, I'll try and release again today with that fix and one other! :D