I just had a look at the blockchain.info page "Most recently mined blocks in the bitcoin block chain,"
and found that 5 out of the 7 most recently mined blocks were "relayed by" BTC Guild.

Am I right to assume that implies theses blocks were also mined by BTC Guild?

And, whilst I'm aware that this is a stochastic process and may not be all that representative of actual hash rate distribution:
Doesn't this look a bit like a possibly problematic overconcentration of hashing power?