It's quite common for startups to have 1 or 2 sexy (and well-enough engineered) projects involving your favorite technology X, to run up the flagpole at conferences or in job ads, etc. But like as not, 80% of what they do (and of what you'll be doing as a developer there) is the same half-baked, post-"blitzkrieg" mop-up work you'll be doing pretty much anywhere else.