Ah, the universal bandwidth-funding debate, and at the risk of the wrath of Danny...
On one hand, we get this great website for free - why shouldn't we pay a bit to keep it going?
On the other hand, maybe it's just a business. OK, internet-based businesses aren't worth much right now, but they were a few years ago and maybe they will be again - hell, after the last couple of years my pension isn't worth that much either but I keep paying into that in the hope things will improve. When the second coming of tech stock arrives (hopefully a bit more sensibly than last time) a website with seventy thousand demographically-impressive users is going to be worth a bit. Without the registered users posting things PPRuNe is nothing at all, so why should we pay anything? Do I get an IOU for the 5% of my output (if i'm lucky

) that's worth reading? No. Maybe all that bandwidth is an investment - risky, but potentially rewarding too - and, as the disclaimer goes, the value of your investment can go down as well as up.
Or on the other hand, maybe it's just a hobby? Expensive things
FWIW, I think Danny's got it about right. Subscriptions don't work if you expect the users to pay to provide the content - i think that the fact that a very financially-savvy webite like the UK Fool doesn't charge tells you something. You can pay a bit towards PPRuNe if you like (personally I prefer the PPRuNe fund for my guilt money, so no personal title). If not then fine, just don't moan about something you get for free.
edit: Maybe Danny should sell shares. I'd buy. Already own part of Southampton Football Club, and i'll never see anything back from that...!