Purple worms have seen a lot of use at my table.
A few times while running the D&D Next adventure (mentioned upthread). Another couple times in the Blingdenstone adventure (And yes, the PCs ran away).
The best use was during a 4th Edition campaign featuring a tiefling sorceress named Nox Amandine. She was the youngest daughter of a noble tiefling family, and they advance politically by assassinating their older siblings (much like the drow). In any case, the opening encounter saw a group of bandits hold up a noble ball, and a purple worm burrowed up and got stuck in the marble floor (becoming a hazard for the encounter, think Sarlacc and you're on the right track). Immediately after the fight, Nox 'accidentally' bumped her sister down the purple worm's gullet.
The purple worm managed to extricate itself, and the PCs found out about a rod that controlled purple worms; one of the bandit leaders had it in his hideout. So they tracked him down, killed him, and Nox claimed the rod. She was clever enough to figure out that while the rod did
summon purple worms, it did not actually control them.
She eventually turned a purple worm loose against her eldest brother, and nearly got killed in the ensuing chaos. The whole party had a desperate fight to get away from all the enemies who were also trying to escape the purple worm while the beast swallowed Nox's brother. Then Nox herself used a potion of mimicry to impersonate her brother while making her escape.
The party later turned against Nox for her criminal ways. The campaign came to an end as Nox escaped captivity and fled town one step ahead of the rest of the party, though without her rod of purple worm summoning.
It's still one of the most talked-about short campaigns I've ever run.
