What about library of elements? Not only openclippart, but custom library. I guess it's very usefull.

I think this has been officially requested on the launchpad site (although I can't be bothered searching for evidence). But in the mean time, I think it's just as easy to save all your "elements" into its own document and then you can open and copy and past the elements out of it.

It goes fine by just drag-and-dropping files now. Do you prefer Fireworks library style?

I'm using inkscape to draw circuit schematics and having a library of elements would be nice. I even did some research on how one could organize such a library in an svg file. There is the "use" statement in the svg standard definition that could suit some of the library needs (much in the way markers.svg is made as I can figure out), but still, this solution has its limits (e.g. if I choose to mirror an element of my library and it has text on it, the text is also mirrored and that obviously is undesired). The "use" statement is appealing because making a change in the original element (e.g. changing the line style) would be reflected in all the files using it, but I guess the standard does not offer the possibility to override some elements' parameters of the used object (e.g. not to mirror the text inside an element), correct me if I'm wrong. This been said, having a library would be a nice feature, and it would be even nicer if changing an element in the library would affect all the drawings using it.

I wouldn't be surprised if allot of people have suggested this before....
Why? because if done well such nested property lists ETC kick butt.... (if i understand you)

Have you seen the styles window from microsoft word? (cant think of which version im imagining or if it still exists)
But anyway....they have (or had?) a styles list that would automatically update and would have styles that would represent EVERY unique set of properties in the whole document.....!

How powerful, how elegant....this idea is mind blowing.....
because its list based and nested..... and you can re-order it and search it....it rocks...

so you can say select objects by any set of parameters...
you could in a few clicks select all red objects with a .2mm outline document wide.... regardless of layer...how big or small...
ETC its like a data base of properties that you can use to select anything by a single click on its style....

I can't praise this idea enough... as it is one that all vector apps really need.......and having one that works well would be such a massive improvement that it would be mind blowing.

I believe CSS support in Inkscape is a roadmap item. CSS would allow the exact behaviour you have described.