I believe having good data is critical to effectively managing a product, but what constitutes good data? Take a look at Eric Ries Why Vanity Metrics are Dangerous to understand why that question is important. Once you understand the question (hint: good data is actionable), you can start to figure out the answer for your product.
Here, also, are some great "top 10" blog posts that are worth checking out:
- Venture Hacks' Top 10 Posts
- Pragmatic Marketing's Top 10 List
- Product Management Meets Pop Culture's Top 10 Product Management Posts of 2009
- Brainmates' Top 10 Blog Posts
- Spatially Relevant's Things You May Have Missed
Disclaimer: Unless otherwise noted, I have no affiliation with linked properties other than being an interested reader, a happy user, or a potential customer: Nobody pays to receive a link. Any opinions of linked properties are their, not mine. I may or may not agree, but to be on this list I think their opinion is interesting.