Here's a great article by Des Traynor, making the point that you have to get the basics (whatever the basics are in your context) before working on the polish, but also the counterpoint that in some cases, polish is part of the basics:
The lean startup movement advocates as little work as possible before validating your business model. Lean is one of those words, like Agile, that are chosen deliberately because they set-up a false dichotomy. No one wants to say they're a Fat Startup. Or that they do Clumsy Development. So everyone is now adopting the Lean Startup® Methodology.
Lean is often misinterpreted as "don't waste time on polish". Sometimes the polish is all that counts. You can't judge the market for a five star hotel by building a seedy motel and seeing how well it performs. In some cases the quality of product is more important than the type. When the interface is the killer feature, it's tricky to go "lean". If your belief is that people will appreciate a fully polished beautiful to-do list, you can't show them a scrappy UI to test the market.
I think there's a very slight straw man at work there, in that the alternative to great design isn't appalling design, but slightly less great design. If you have a decent designer, they should be able to put together something much better than the wGet UI Des presents as a "lean design", in a relatively short time.
Going from good to great is still a lot of work, but perhaps it is possible to partially test the market for a 5-star hotel by leaving the golf course and the spa till later.
Final point: Lean doesn't advocate putting out crappy designs, it advocates doing the minimum that works to test your hypotheses. If design is indeed necessary for the assumption you're testing, then it should certainly be on your to-do list.
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