Who designed the graphics for your web app, and where did you find them?
tdonia: typography.  it's not the only thing a good designer knows, but it's a basic skill that the good ones respect.there are 2 schools of design that a savage like me can comprehend: systemic and emotional.  i'm sure that many can argue for the many gradations, but these are the important distinctions/extremes to recognize. that said, it's not either or - successful designers evoke (that's an important word- what does your potential designer's portfolio evoke) their ideas in a consistent/lasting manner.  this requires both schools of thought - powerful ideas that can be repeated/propagated.emotional design is provocation.  vimeo is better at this than google - compare the persistent vimeo login page with the occasional google holiday logo.  that said, there's a much wider range of emotions that neither of these places touch.  good emotional graphic designers will understand how to communicate your product evoking a positive emotional response.systemic graphic design is the ability to maintain an identity, consistently, and create familiarity.  most of us feel that if we were hired as a brand manager for google, we'd have a pretty good sense of whether or not a page put in front of us meets their identity's requirements.  that's a test to remember.  more than any one event in your brand's lifecycle, systemic graphic design will be there to give you a (relatively) easy solution in any situation, once your voice has been defined.  best example in a typeface: helvetica.  these designers demonstrate a comprehensive understanding of systems design.  look at Paul Rand's work & Josef Müller-Brockmann to see evidence of a system that's designed to be familiar, even when it's radical.ideally, you need both.  an easy metric that would hold up against the best ones i know (and no, i won't release their names, they're busy ;) - they love to talk about their art and they will not hesitate to tackle a new challenge, especially if it seems hard.  even at the expense of dayjobs & prior commitments.  then, give them space.  when ideas seem ethereal, be very clear on your business requirements, but let them solve the problem/bring it back to earth.hope this helps.  graphic design is half of how i discovered (social) hacking and i can't stress its importance enough - it's a useful field to learn about, not just depend on.