Extensibility - Plugin system?

[Quantum7]

I've looked at hundreds of different software products during the 20 years (roughly) I've been interested in software & software development.

One of the key feature's I've seen in alot of the products that aren't aimed at one specific market but allow alot of user flexibility is some kind of system of allowing users to create their own plugins for the product.

What's your (kinook's) vision on this? I haven't seen anything like this in the road map, so I assume it's not anything planned (yet) in the short-term.

Main advantages seem to be:
- It allows the developer to focus on the features dealing with the main functionality.
- Speed of development. Extra functionality gets produced without costing development time.
- It prevents alot of feature bloat. Lots of features can simply not be installed, thereby simply not being present in the software.
- User interaction. Often hundreds of plugins arise, greatly extending the possibilities of the application. Which again attracts more users, who create more plugins =).

Ultrarecall seems to be especially suited for this kind of system. I.e. for viewing different kind of file formats (as directory opus uses plugins for).

Remarks
The best way I've seen this done is in a way that the user has an options window inside the tool in which he gets a list of possible plugins, including a short description of what they do. He can the check which one's he want / doesn't want; those get installed / deinstalled.

Some examples (based on what I still have installed ):
- Winamp
- The Bat (ancient e-mail client)
- Meedio (got bought by Yahoo =()
- Directory Opus