Btw it's not only transfer problem, calculating complete block for every share is pretty hard, too. Forgot that pool can calculate tens of hundreds shares per second...
So you're saying that a small set of pool systems scales better than the idle CPUs of thousands of miners? Thats silly. As the txload rises miners can simply prioritize transactions based on their hash distance from some random value, allowing TX validation to scale far beyond what the pool could support.
Today the responses to take about 181 bytes on the wire. Blocks are frequently about 4k, so at the moment difficulty would need to be 22 to send the whole block and use the same amount of traffic. If it were compressed by only sending the TX ids, it would be 354 bytes/share for 10tx shares, or less then double now.
Someday in the future when blocks are 1MB (the largest size clients will accept today) the 'compressed' size will be 128032 bytes/share. Share difficulty would need to be ~750 to get to the _same_ traffic levels we have now.
This could all be further reduced by miners only sending incremental updates. So basically in that case it would only take resending each TX, along with one extra per per new block (~6/hour) to setup the root. Done this way it should do no more than 2x the current bandwidth, though it would take more software to track the incremental work per miner.
But even ignoring all the things that can be done to make it more efficient: at current bulk internet transit prices ($2/mbit/sec/month) full 1MB shares would each cost the pool $0.0000064 each.
Assuming 2MH/J, $0.05, and an exchange rate of $6/BTC GPU mining won't be power profitable past difficulty 10,000,000, even for people with cheap (but not stolen) power, assuming the current exchange rates. At a share difficulty of only 12 this would be bandwidth costs of only about $5.33 block solved while sending full 1MB shares without any efficiency measures. If you can't figure out how to make that work then I'll welcome your more efficient replacements.
(the formula for breakeven profitability is
diff = (719989013671875*exc*mhj)/(17179869184*kwh)
where diff is difficulty, exc is the exchange rate in $/BTC, MHJ is the number of MH per joule, and kwh is $/KWH)
As I write this deepbit is down and the network has gone 30 minutes without confirming a transaction. This is nuts. I don't think the bitcoin community should continue to tolerate the reliability problems created by large pools. You're free not to participate in an operating practice, but the network is also free to ignore blocks mined by pools which actively sabotage the stability and security of the network.