You'll pry my books off my cold, dead body. By the time you shift them all I'll be flat and dessicated.
How annoying were Eustacie and Ludovic? I cared so little about their fate and mostly did not find them amusing. I know they are a parody of young romantics and serve as a foil for the older and more sensible couple, but I really wanted Ludovic to get slapped at certain points where he insists on recklessly endangering everyone else for no better reason than his own boredom and fecklessness.
Fortunately for me, Heyer, though more tolerant of young bucks than myself, couldn't take an entire novel of Ludovic and Eustacie, either. The real romance here is between Tristram and Sarah, two intelligent and somewhat older individuals who thought they were too sensible for romance. And thankfully, Heyer didn't choose to illustrate their growing affection by having them behave like a pair of irrational idiots (something most romance writers seem to think is evidence of strength of feeling) but by making them more clever and amusing as they grow closer and learn to play off one another's strengths. You can almost see Sarah and Tristram blooming with happiness as they shed boredom and loneliness that they hardly even noticed themselves suffering.
Come to think of it, it is probably that elevating happiness that allows them to be so tolerant of their annoying young foils for the length of the story...