For me, a startup is something you throw everything into: time, (your own) money, and aggressively focus on. It's filed, you have customer focus, and you're not doing it as a hobby. Sorry, I'm over the "startup" (project) that's building something fascinating...but has no focus on generating revenue. It's a hobby. Not a startup.
It seems to me that the two are interchangeable, because often startups are add-ons/features of existing infrastructure; and this could equally be a project.
Especially in the age of Facebook Connect, I am becoming increasingly wary of trying out most new apps because I'm having difficulty gauging the motivation of the founder(s).
In truth, I usually go through several pages of an app's development blog before I even think of trying something out. If there's no dev blog, I generally assume that it's just a "project", and not something that will grow or change too much.