Tempted now, but still holding out, since already have an Excite 7.7, TF300, Nook HD+ (great with CM 10.1), iPad 4 and S4. The S4 has a fast chipset too, great 5" display, works great with Bluetooth controllers and HDMI, so will use that as a "Shield" for a while until I see how reliable the Shield is with users. I looked at the Ouya, but the lack of storage space for apps, proprietary market and the S4 blows it away for the same function means a "pass" for me.
Added: The Shield should be a great emulator device due to the Tegra 4. Hoping more MAME games play smooth on it. The gap now with a T4 tablet is greater since the Shield price drop, so more tempting.