Yes, I'm using the contact us, reporting, and anything else the app offers. Every app...
I have the habit of contacting developers for apps I have installed in my phone, by email if possible (since Twitter's limitation in number of characters prevents me from being able to describe the issue completely). This is the first thing I do, not to criticize the developer but with the hopes that what I'll be saying would help the developer "develop" his or her app further.
If the developer doesn't respond within a week, then I'll probably leave some low rating, but still with a justification as to why the rating was such so that the developer may still know the reason. But if the developer responds to me in some inappropriate way (it has happened already), then I'll report to Microsoft under the correct category.
For apps that are fraudulent, misleading or have down right poor performance (such as apps that contain a mere collection of hyperlinks or apps that say they do something whereas they really don't), then a report is immediately necessary.
I'm not reporting every app that I have just because the same app in another platform is "better" - I'm not a programmer and I have no idea how easy or how difficult it is to even meet my own requirements for a "good" app. Luckily there are developers who offer BETA programs for their apps where critical users should participate for constructive comments and collaboration. But unfortunately not all developers are as generous (or as liberal with respect to available time) - who's to stop them from silently marking a persistent complainant's email address as spam?
It would be kind of interesting to see the list of apps grow in this thread, but whether Microsoft (or the relevant developer) sees it or not isn't guaranteed.