I had some better luck today. I updated various drivers from the Dell site. I assume the most significant was the Wi-Fi driver. Now I'm able to connect to both the Actiontec and Netgear PTV3000. But the display is only in extended mode - clone mode curiously doesn't work. And extended mode on a tablet is not very useful as there's no way to move the cursor over. Let's see if upcoming patches help. I'll keep trying.

I ran into similar trouble and found by running dxdiag (and saving the full results to a text file and searching for Miracast) that the WiFi driver isn't compatible with Miracast.  Since it is listed as being Miracast compatible in a couple of places on the product description I felt obliged to call Dell support and let them know. 

Through research I have found that the WiFi driver that Dell has made available for the hardware is not NDIS 6.40 compliant, so hopefully they can provide a simple driver update to make this advertised functionality work.

Same problem too.  Can only use extended mode which makes it useless.  I hope they get some drivers updated soon, or I will have to return it as I bought it for the primary purpose of using maracas to my TV.

I have the same problem. I'm very disappointed. I believe that's false advertising because I have seen it work in 2 dell venue 8 pro commercials.

Same result here (it connects and can Extend but can't Duplicate).  Also it's annoying that the screen orientation of the Venue 8 Pro itself is forced into Portrait mode when "projecting."  This seems to be due to "auto-rotation" being locked when extending the display, and its default orientation is portrait instead of landscape.  I'm kind of curious is that might also be the reason for not being able to Mirror the display.  :S

Same here.  I can duplicate, but it locks at 800x600 in the middle of the screen.  There's no way to change the orientation... really frustrating.  Any word from Dell?  Miracast is totally useless in this state...

I am also having this problem, miracast is the main reason I purchased this product and it is ridiculous it is not working correctly and we have no response of a fix coming.

Bad news guys!  I just spoke to Dell tech support and it doesn't look good.  After waiting for about 40 minutes on hold and being transferred 3 times to Venue Pro "Specialist" it truly hit the fan.  Not only did the "Specialist" not know what Miracast was, but he asked me to spell it for him and acted completely bewildered.  I asked again if he was a Venue "Specialist" and he said yes.  I then told him to please read the product's box where "Miracast" is prominently displayed and I then had to explain the technology for another 5-10 minutes.  When I told him about this forum post, he went silent.  I told him to google "venue 8 pro miracast problem" so he could find it.  He literally just stopped talking...seriously.  I just said goodbye and hung up after about a minute of awkward silence and mumbles.  I have lost all hope...lol.  I think I might order the Asus T100 tomorrow because it has an hdmi out.  Ugh.

Same problem here.  I have updated the drivers.  I am using the PTV2000, which works fine with a ThinkPad X1 and 430S running Windows 8.1.