I've been living with no WIFI after waking up for a while. For me, I'm pretty sure it's a driver issue. The SP3 shipped with bad WIFI drivers, and I believe they have fixed the driver, but the SP3 seems to not always use the new version of the driver.
Here's my history:
I had the issue after purchasing mine on the US release day. I bought a new high-end router, which made no difference. Then it just went away after one of the updates and was fine for several months. Then I did a reset, and the problem came back. I called support, and after about two hours, they decided I needed a replacement unit (I was skeptical). Received the unit (a refurb), which arrived with no updates installed, and had the same problem out of the box. After installing all of the updates, it STILL had the problem. So, I sent it back.
I have tried numerous fixes found here, including manually selecting the latest WIFI driver. Finally, a few days ago, I was messing with the manual driver selection and I did this: 1. Manually selected the latest WIFI driver in device manager. 2. Repeated the process, but selected "Search automatically for updated driver". BAM! My problems have gone away again.