It occurs to me that the simple definition of novel versus novella could usefully be updated to account for ultra-sized works of fiction, those titanically-proportioned books so often taken to be the defining criterion for admission into the Serious Novelists Club.
Ulysses, The Corrections, Jonathan Strange and Mr. Norrell: All are books wide enough to carry the author's name horizontally across the spine when shelved.
HP and the Order of the Phoenix, Infinite Jest, Moby Dick: These are the kind of books that furniture removal men hate, but which can also be used as furniture (small stools, door stops and so on).
At present we have the short story (small), novella (larger, but still small) and then the novel. Perhaps we need a new word for the type of 600 pages-plus book that will concuss a Chihuahua if knocked from the kitchen table...
Like comedies at the Oscars, short works often seem overlooked in the canon of Great Novels, physically dwarfed on the bookshelf and struggling to compete for critical attention. We seem impressed by marathon efforts. Short stories, on the other hand, get relatively short shrift.
The organisers of NaNoWriMo say "we don't use the word "novella" because it doesn't seem to impress people the way "novel" does." They're right. Which is a shame, as there are some wonderful writers out there who rarely, if ever, overstep the 300 page mark.