Des Traynor, whose articles have been featured on swombat.com before several times already, posts yet another article worthy of your time. This one outlines the dangers of bad data visualisation, which is just as pernicious as bad data analysis.
Your goal when designing with data is to make large volumes of information easy to digest. That doesn't mean you hide details, it means you make it easy to find the important ones. If you don't know which ones are important, then you need to find out before you tackle the design.
The real genius in data analysis is knowing what questions to ask. Everyone wants sexy charts showing sales, or revenue. High and to the right, right? There are so many useful questions that go unanswered, and that's where data visualisation can help.