I personally have over 30 plugins that I guarantee are working in 1.8.

Chances are, if you can't get anything to work - you're doing something wrong.  As far as whether something is useful or not depends on your specific needs.  Don't just go throwing in plugins for the sake of it, build a thought out set of functions that work to a specific goal.  Also, some plugins conflict with others, don't install a bunch of plugins at the same time - do it one at a time so you can properly identify issues with plugin order and genuine mutual exclusivity.

Regarding the developers, some are experts, some are amateurs, some are in between.  It's an open source community with almost zero quality control.  The onus is on you as the end user to decide which developers and plugins to trust.

nothing useful, and working as well

Well, that's not true. Developers like speedy snail, Matt Beckett, iionly, Kevin Jardine, etc had developed pretty good elgg plugins for elgg 1.8. 

Elgg 1.8 is moving really fast and developers are adapting and releasing tons of new plugins every week. 

Just browse, do research.

Rodolfo Hernandez

Arvixe/Elgg Community Liaison

there are lot of good working plugins in 1.8. if its not working in your case its your problem of not installing properly...