There is an app on the Marketplace dedicated to this task - but what is the most effective way to channel your feedback to Microsoft about Windows Phone 7?
Being queried by an email from Robert N, Paul Thurrott decided to direct the question at Microsoft directly. Since they have a dedicated section on their mammoth of a website for Windows 7 feedback, there isn't a strong argument as to why they don't have something similar for their latest mobile product.
Instead of one place to allow easier digestion and storage of feedback from a growing user base, Microsoft have a few ways available to get in touch with them and voice your opinion(s). Paul listed these locations as Microsoft Answers, Windows Phone Backstage Forum, Facebook, and Twitter.
Although many of us would prefer a single location, the above alternatives aren't so bad at all. Activity seems to be relatively high on their Facebook and Twitter, however, this does not provide the correct platform that is required for Microsoft to engage with their users. Hopefully, this will be fixed sooner rather than later, since WP7 is at the early stage of deployment where there is a huge amount of feedback available.
Source: Windows Phone Secrets