In Ubuntu 11.10
I cannot open and save a new folder in the library Browser via -usr > share > librecad > library in order to "save as" a block in.
Blocks are only usable in current Drawing - I know this is an improvement request (and needs to be added in "bugs" but it ties in with txtinmans post)!
see:
http://librecad.org/cms/home/get-help/forum.htmltxtinman - you can re set your "relative" zero point to where you want, first by going to snap > relative zero then you can pick a new point in your drawing * if your new point needs to be on your existing block, you will first need to "Explode" it (break it back down to separate entities) then using the snap tools you can snap onto a desired position on the block!
once you have done all of that you:
1. Select block in block list.
2. Click on "insert the active block".
3. Then using the snap tools "restrict" Horizontal or Vertical you can insert your block relative and in-line with the first block or relative to where ever you set your relative zero point!
Hope this helps
cave