This is actually one of the biggest things I appreciate from studying Marx: the reminder that 'use-value'[1] and 'exchange-value'[2] are two, separate things, and while I generally want things based on how I can use them, the market doesn't care about that at all.
Startups would be wise to heed Marx's words here, and remember this difference. Your job as a startup is to make money, which means producing something that has a high exchange-value. Don't let your own notions of use-value blind you to what the market cares about: exchange value. How many times have I said "That idea is stupid, I'd never use that" and then it became a smashing, overnight success? Too many to count.
1: Basically, "how useful is this thing to me?" http://en.wikipedia.org/wiki/Use_value
2: Basically, "how much could I sell this for?" http://en.wikipedia.org/wiki/Exchange_value