In response to the OP, yeah, bashing something/someone b/c they made a different choice is pretty weak (xenophobia anyone?).
I won't *bash* the 4GB choice and I certainly won't say anyone is wrong for making that choice, but I honestly can say I don't understand it -- either economically or practically.
I'm sure people have really good reasons that make sense to them for going 4GB or 8GB...I went 4GB and first and decided to upgrade.
I originally bought the 4GB, thought I could live with it (much along the lines of the rationale espoused in this thread: my music library is 30GB, I'm going to have to triage anyway, why not save the $100?). Well, I triaged and found that 4GB for music, videos, photos just wasnt enough even with the most parsimonious of selection policies. Further, I wondered what would happen if 3rd party apps, file system support, et al were ever released. Wow, then I'm really screwed. I returned my 4GB and ate the $50 restock and scored an 8GB. Much happier!
First, the iPhone is not really a poorman's device (or poorwomans). In the grander scheme of cost of ownership $100 is statistically insignificant. For someone to argue that $100 of fixed cost up front on an item that not only is already $500 and incurs an atleast $60 monthly recurring cost (even more when you add regulatory fees and taxes) is really an uphill argument -- tenuous at best.
Second, consider the economics: $100 for 2X the flash? Apple either seriously upcharges on the 4GB or discounts the 8GB...either way their margins are NOT the same on both devices. My inclination is that the 4GB is upcharged (would make sense from a GP perspective). If you really want to make the "value" argument, you are getting more back for your buck with the 8GB.
Finally, it's usage. I couldn't fit my shuffle mix, recently playeds, 4 episodes of the office, and my last 2 months of photos on a 4GB. That's what I want my device to hold (that's just me, remember, YMMV) -- that cinched my decision to upgrade to the 8.