Personally, I have a 12" Powerbook and a Panasonic TH-42PD50U 42" ED plasma which can be had for $1799 and 0% interest till 2007 at Circuit City.com (and probably cheaper elsewhere). While I think that a powermac and a 23" or 30" display are very nice, I in no way think that they compare with a nice plasma. If you are looking for a Home Media solution I would get a nice 42" or 50" ED or HD Plasma.
Plasma vs LCD
Plasma screens are heavier, thicker, will operate for less hours overall, and have a darker picture than LCDs. But are cheaper, have better black levels, don't suffer from motion blur pixilation, and have wider viewing angles.
LCDs are much more expensive, have inferior black levels to Plasmas, suffer from ghosting and motion blur because their response rate is slower, and have narrower viewing angles. But will last longer, are thinner, and have a brighter picture.
While I am in no way an expert (please don't flame me) these are generalizations that I picked up while researching at
http://www.avsforum.com
As far as ED vs HD:
HD is obviously better but at what cost? Currently, you have to pay $10 extra per month on top of digital cable to get just a few channels of HDTV. For the most part, TV just isn't there yet. As far as DVDs go, you have to have a Blue-ray or HD-DVD player which will run over a thousand dollars with little to no content available. This content and players will become available in the next few years, but you may not want it because you will be able to have TV / Movies on demand from an iTunes Media Store from Apple. In other words, I think that once again convenience will trump quality and HD content will not take off because of the introduction of more convenient web-based content. (Which of course, will take years if not decades to go HD because of infrastructure issues)
For these reason, I chose to buy a 42" ED plasma, a less expensive Mac, and am eagerly awaiting a MacMini/FrontRow DVR combo or an Airport Express 802.11n that will allow me to stream video content downloaded from my computer. (This only requires the networks/movie studios to play ball with Apple which sadly, it seems, may take some time.)
I wouldn't blame you for buying a G5 and a 23 or 30" screen but I don't think they are the most elegant solution for a media center at this time nor do I think they could ever replace a big beautiful plasma screen. To each his own though I guess...