... so here is my story, as I put into an email for a friend:
So you have to realize, when I entered the BTC game I was basically looking for free videocards last Aug/Sept timeframe. Then coins were a little bit above $5 (falling from $7). I was figuring if I bought $30 mobos, $80 power supplies, and GPU's for $100 each I could pay off a rig in 3-4 months. Everytime it paid itself off I have just bought more video cards (why not?)... oh and I did mine $600 USD worth for my vegas trip, that was nice!
So I started with 3 cards.
Now at 14 video cards (will be 18 once I get the latest rig running, still have two cars in the mail!) and with the rise to $9/coin I'm up to $20-30 a day. As for GPU investment, payback can be $1.50/day per card if you buy cheap $100 cards it refunds their own purchase in a little over 2 months (assuming you already have a PCIE slot and PS wattage to spare). Or when you are at my level, when buying two cards I can pay that off with my total rig power after as little as 7 days.
So, that's how I see GPUs.
ASICs will be a revolution. The question is how fast. When BFL announced their FPGA's they claimed "custom" hardware and twice the output and four times less power than what was actually released. Problem was it is off the shelf FPGA hardware with custom interface - performed 50% the originally advertised output(mhash) and took 4x more electrical power. Oh and they were 3 months late ... on the first batch! So BFL claims October. How fast once they start producing are they getting units out... wait nevermind there is a waiting list... and last time unless you get in on batch #1 you are waiting ... 2-3 months maybe? So my wild guess is if you order today you will get your ASIC in 5-6months.
Problem is even if the hashrate goes up the network automatically increases difficulty so the "rate" of coins released (~7K coins per day, soon to be ~3.5K in DEC) will adjust to be consistent, and how much profit you make will be dependent on how early of an adopter you are (first guys in will make huuuge bank for a couple weeks/months - if coins hold their value, dumping the market will make prices go down). If you have 10000 people with ASICs as big as yours or bigger then that payback starts to become a lot longer. If you were get the first 120Ghash rig today you would be sitting around 1/150th of the whole network I think? (if my math is right!)
So if history tells me anything, the real unknown is the reward getting cut 50% in December! ASICs are a wildcard for sure, and eventually will be the future of bitcoin, but I'm not betting on BFL quite yet.
Right now I am in the process of upgrading cards, so if I do have to sell later I am selling Radeon 6950s - 7970s which will hold their value as they are still rather useful to gamers. The old 5XXX cards will probably drop like a rock in price (only $90-150 now but get same/better mhash as a 6-series card). Problem is 7970s are $350-400 and take twice as long to payoff - but will host value the best.
Eh just my $0.02BTC