Got this in my email just now:
New Reply has been added to "Please support Grain - GRA in Cryptsy!" by Marinecoin
Attention:
Our agents have been monitoring this area.
agree amongst yourselves and donate %20 of your network's Hashpower to the common network.
We are taking down BTC and crush it to its knees, take away its throne. We will diminish its value to the cost of electricity. We have the ultimate plan and the capacity, there is a war going on and we need a pact. Your currency will soon be traded on our exchange at top value.
Maritime Global Crypto Network
The Central Agency of All Altcoin Exchange
I think that is no good idea. First damaging BTC will make the big investors afraid of investing in any coin. Because when this can happen to the biggest one it can happen to all coins. And second you dont know what they are really doing with your hashpower may be they need it for hacking or something other bad.