I've lost extended attributes of files on a number of systems because they aren't always included by default in file operations. I don't trust everything that could possibly write/update a file to preserve them--common 'safe' pattern is to rename as .bak and write new file contents without EA to original name. Nor do I trust myself from archiving without using the right options in a hurry.
Yes concerning. The possibility of losing them between filesystems is worrying too.
One rule of thumb is `mv` will keep the attributes by default (given similar filesystem) and everything else needs tweaking/extra args. There's a section on it over here: