I get it for the geek factor, but apart from that, I don't see why anyone would bother. Let's look at the two solutions:
1. If in worst case scenario you don't have any free HDMI ports in TV/projector, pull cable out and plug in laptop (if do have spare port, then can just keep spare cable around for this).
2. Set up network video stream on laptop/PC, find stream on PS3.
Scenario 1 means no transcoding necessary, no network bandwidth is used up. Scenario 2 requires use of two machines, and if you want to broadcast at a decent level of quality is going to tie up a decent sized chunk of your home network bandwidth. Setup time with both scenarios is roughly equal. You mention streaming to multiple machines at once, just how many PS3s do you own! 
Plus, if it's something you do frequently, you'd be far better off with investing in a proper HTPC (running XBMC or similar) and cutting out all this faffing about.
2 ps3's 1 htpc, 2 hdhomerun boxes, 3 xbox360's. 1 Media server

It's not about hooking up a hdmi cable. It's the fact that I only setup my home theater once period. I don't have to touch it again. so by your own logic hooking up a laptop is more work.