I don't have any new issues on Lion -- well that's not really true. I have had to force quit EyeTV now and again and never had to do that before. I do occasionally get a zero length recording every now and again, but that used to happen on Snow Leopard as well (Lion used to do that as well, if memory serves).
I have two different setups. First, iMac 27" (Late 2009, Intel Quad-Core i7, 2.8 GHz, 16 GB, ATI Radeon HD 4850 512MB). Second, Mac Mini (Mid 2010, Intel Core 2 Duo, 2.4 GHz, 4 GB, NVIDIA GeForce 320M) connected to HDTV via HDMI. Each setup has two USB tuners and is running Lion 10.7.4.
I'm running the Mac Mini at 720p and letting the TV upscale the image. It looks good. I used to run at 1080p but all the Mac's text is just too small to read at the resolution.
I used to have image stuttering issues when I used a Mac Mini mid-2007 (Intel Core 2 Duo, 2.0 GHz, 3 GB RAM, Intel GMA 950). But that machine just didn't seem to have the horsepower: either cpu or graphics to drive an image to an HDTV at 720p.
I've read somewhere on this forum that sports playback is very demanding and I've found that to be true. I saved a clip from the 2010 NBA finals and found the Mac Mini mid-2007 just couldn't render the image smoothly. This clip on the Mac Mini mid-2010 renders more smoothly -- I can't say it's perfect but it does look better.
I know more about this stuff than I should.