I largely enjoy Shadowplay so far, and I run it 24/7. Still waiting for that Twitch.tv integration right now, since I still have a Twitch account that is working. Once some awesome stuff happens I'll edit it and post it up.
Just a note to anyone trying to figure this out and Shadowplay isn't working in-game...it requires fullscreen BS that honestly annoys me. And specific NVIDIA Experience settings for some games.
On average, you'll be look at a 3-5% performance drop in BF4, whereas with FRAPs you'll be looking at around 8-15% given that it is more dependent upon your CPU. I went from an average of 46 FPS to 41 with Shadowplay turned on manual mode. That's maxed out with NVIDIA experience options turned on (Fullscreen, all Ultra, MSAA 4x 1920x1200 on a GTX 670 and 2600k @ 5.0Ghz). The lowest FPS in multiplayer games was 25 FPS (whereas before minimum was 27 FPS), pretty close to the 24 FPS that most humans are used to watching. The highest was 89 FPS versus 92.
Recordings have a better compression rate with Shadowplay, about 20m of gameplay is only 4-6Gb with x264 encoding. FRAPs will run you around 20Gb for the same period of time recorded, a terrible 1:1 ratio if you are using an SSD for the Shadowplay recordings folder.
SSD does increase read/write performance, but it is negligible overall with Shadowplay, my 2Tb WD BE performs just fine without noticeable hiccups in performance.
Streaming to Twitch is effective, giving better quality then the Twitch streaming program IMO, less graininess in the image.
I have no clue how to use Vegas or anything else really for editing videos. Anyone who can help with that is much appreciated.