Well, I've kept having problems after all.
So, I kept searching. Factory-reset my Airport Express, tried numerous combinations for WiFi, but alas nothing worked. Home Sharing kept dropping out.
Tried turning off Bluetooth and all bluetooth-enabled hardware, but it still crashes.
Changed my modem, bought a router, a complete PowerLine network, and plugged everything via RJ-45 cables. Everything plugged well, got everything working properly - Internet, streaming, etc... I was pretty certain that it would resolve the problems. Nope! Still dropping Home Sharing!
My big problem is once Home Sharing drops, I need to quit iTunes to restart it. When I do, very often (80% of times), the iMac will freeze, spinning wheel and all, can't start any more apps, I need to reset the computer by powering it off. -THAT- is what really upsets me.
What does it take for Home Sharing to drop? Streaming an HD file 2+ gigs, and after about 10 minutes, it just freezes. That's when I know that it's game over, and I need to go downstairs to my iMac, quit iTunes, and if it doesn't freeze, restart it. But like I said, most of the time I need to reboot the computer with ON/OFF switch.
Again, all this started shortly after a thunderstorm which caused a power outage in my area. Which was also a week or so after OS X Lion was installed on my iMac. Not sure that it is Lion that's responsible, since many people with dropped Home Sharing are on PC's and Snow Leopard I think?
So, stop tinkering with your WiFi stuff, I've spent countless nights playing around with it, and it doesn't change a **** thing. Especially that plugging the AppleTV on my home network via Ethernet cables hasn't helped things at all.
I'm extremely distraught with all of this. I just don't understand what is wrong, and what else to do!!! I've owned computers since 1981, and Macs since 2002, and I'm really at a loss here.
I really hope someone from Apple is following this thread. I would love to send any logs to help solve this problem!