Seamless Pattern extension V0.6. Updated 8/9/2015
Vídeo a bit outdated :(
Inkscape 0.48 and up.
Install 4 files inside the extensions dir.
You can use it like a procedural template or like extension.
You should not modify the layer structure of a seamless pattern.
You can share the full pattern into different documents.
Opacity could overlap objects if not in full pattern
If you convert the seamless pattern to a "real" inkscape pattern with Objects->Pattern->Objects to pattern, you can't edit it again in a seamless way, so if you want to try, try with a clone of the pattern, or in a new document.
Only works in Inkscape, not browser-compatible, so you need to export as png.
Thanks Maren for the translation and fix strings!