You'd be surprised - they're really not bitter at all. They're a component of lots of Middle Eastern poultry dishes & a few French.
In all the dishes I've come across, it's the rind that is used the most - the pulp is scraped off & discarded. Couldn't find the TNT preserved lemon chicken recipes I used with a brief search, but will say that they turned out well. The lemon flavor is definitely intensified by it's salt curing, so a little goes a long way.