I have a background in branding so I don't want to throw cold water on this post, but you can take things a step further: For a startup your product is the most engaging aspect of your brand — so get it right.
It's a bit more than a "useful product" — for example an engaging game like Farmville isn't "useful" but it does quite a bit of brand building within the product. In many ways you an give software a personality (example: gamification), and those little touches might not be useful in and of themselves. A good real world example would be that the old Macs booted up with an icon of the computer with a smiley face — that wasn't useful but it was a great brand building exercise. Contrasting with that Acer did the same thing with their monitors and their logo was so ugly it made the brand cheap.
I think the product is the obvious part of brand experience and the one that most startups think is the silver bullet. It isn't...there is no silver bullet. It is about delighting people every single time they come in contact with your company.
In a B2C context, the only contact the user may have may be the product in which case focusing the brand experience around the solely around the product may make sense.
In a B2B context there are touch points such as support and customer service, billing, development, etc. Whether you know it or not, you are have the opportunity to build a relationship with that customer at every single touch point. If they have an experience that blows them away at every time they come in contact with your company...this is something that goes way beyond just having an engaging product. This is something they will want to tell others about.
3. Creating a genuinely useful product.