I just read Matt Asay's article "Time to upgrade upgrade open source perceptions of Gartner" where he gives Gartner credit for finally getting open source. His point is that Gartner has stopped steadfastly arguing that open source's impact was negligible. On that point, I have to agree. Gartner has jumped onto the open source bandwagon just as it was accelerating out of Gartner's reach. But what does that really mean? It means that Gartner's readership (predominantly technology vendors) have forced Gartner to cover a market segment that they are no longer able to ignore. It also means that some of the open core software vendors have gotten big enough that they now represent a decent market for Gartner reports and services.
From a technology customer's perspective, the value of Gartner's (and most of the other major analysts, for that matter) opinion is pretty much the same. Main stream technology analysts focus on the business of technology (market share/cap/potential) — not the design or suitability of the products. Market analysts don't work with the technology. They don't talk to users or developers. Half of the people they talk to are CIOs who couldn't identify the user interface of the software they are discussing.
So, if you are a software company or an investor trying to figure out where to spend your money, Gartner's reports just got a little bit more useful. If you are in the market to buy technology, Gartner won't help you understand your requirements and what product is the best fit for your organization.