I've eaten my fair share of vegetable "pastas" in the past. While slivered carrots and zucchini are not necessarily a bad thing, they're not a true substitute for their starchier cousins. In Try This at Home, Richard Blais's has a number of what he calls "impastas," including this Potato "Linguine" with Conch and White Wine, which is actually brilliant.
'conch' on Serious Eats
Blais has a number of what he calls "impastas" in the book--most are in the "I-wouldn't-mistake-this-for-pasta-any-day" camp. However, the potato "linguine" stands out. He first made the dish on Top Chef Masters (those viewers among us will probably remember the chef-testants doing their best to look cool cooking in bathing suits) and appeared to fool the judges into thinking that the potatoes were indeed freshly made pasta. Indeed, russet potatoes make ideal pasta substitutes, as they are mild in flavor and high in starch. Mingled with chopped conch (or clams), parsley, oregano, and bread crumbs, this "linguine" is more than just a substitute for pasta.