We can be fairly sure that Mt.Gox is ware virtually all minted coins get liquidated by miners and Mt.Gox addresses are know so it should be possible to see what percentage get sold basically immediately and what percentage get put in storage. Then see if that ratio changed around February.
Extremely unlikely. Aside from that there aren't that many ASICs out there yet (GPU mining is once again extremely profitable, too), 25BTC * 6/hour * 24 hours = 3,600BTC are being created every day. Even if every single miner immediately sold everything they mined, that would still mean that sale of mined coins accounts for 3,600/72,465 = 5% of daily MtGox volume. If you take into account all currencies traded on all exchanges, the percent is closer to 3,600/190,000 = 1.8%. So, miners don't affect the price of bitcoin almost at all. Never have, really.