(a) We actually can be pretty damn sure adoption is growing, unless you willfully ignore data (or start dismissing sources without any evidence to motivate that dismissal)
I agree that adoption, in any reasonable sense, has grown between 2013 and 2014. However, I see no clear evidence of it growing since February, and some evidence that it is not. Given that through 2014 there was substantial increase in the factors that are supposed to push the adoption -- penetration of BitPay and Coinbase among merchants, venture capital investment, promotion in the media, etc -- that stagnation in the numbers cannot be just statistical noise.
The evidence people usually give is the number of transactions, number of blockchain.info wallets, and the number of merchants "adopting bitcoin". I have explained before why those data are not reliable and do not really measure adoption. I have also pointed to the presumed BitPay.com wallet which does not show inceased inputs since February.
Moreover, note that the number of transactions has been steadily increasing through 2014 while the USD volume (minus changebacks) is stagnating. So the average USD per transaction is falling sharply. That seems easier to explain if most transactions are non-payments.
Trading volume (in USD) over all USD exchanges, last 2 years:
And the same for CNY:
Trading volume is not related to adoption. Consider China, for example, where usage in commerce is null, and yet has many times the trading volume of the rest of the World combined. Or note that the peaks in trading volume occur when the price is changing fast, up or down; why would that trigger a frenzy of bitcoin spending in commerce?
1) USD tx volume is still below the peak which isn't such a surprise considering that it shoots up during a rally / at an ATH, but more problematic is
2) it is growing only at a rather comfortably slow pace (NB: linear chart)
USD tx volume should be a reasonably good measure of the 'medium of exchange' aspect of Bitcoin, because for most goods purchased, the unit of account in which the goods are priced is USD, so a growing USD tx volume despite falling prices is a sign there is more medium of exchange usage - but it's not exactly skyrocketing either - since the middle of this year, it's been steadily climbing up (despite falling BTC/USD), but not going through the roof exactly either.
Well, to me this chart does not show any growth at all in 2014. There were some small peaks in June and in the last few weeks, but they did not reach the levels of Jan--Feb 2014, and the volume quickly returned to the baseline that has been in rule since March.
But, anyway, even this chart does not show use in commerce; it is merely the total BTC output of all transactions (minus estimated changebacks) times the BTC price. So it includes an unknown but large percentage of non-payment transactions. Perhaps the USD volume of payment transactions are increasing, or perhaps it is decreasing; we cannot tell from that chart.
I insist, neither blockchain statistics nor trade volumes give us any useful insight on actual adoption as means of payment. The traffic in the BitPay and Coinbase "wallets", as gathered by that Czech site, would be a more direct evidence (assuming the wallets were correctly identified, which I cannot tell for sure). As I wrote, I have had a look at the Bitpay wallet, and did not see growth in 2014 either. But please check yourself.