Finally caught up. A few observations:
Mike tipped Lydia off that the DEA were about to walk into her office. While this was seemingly pointless as she had less than a minute to react, it's surely evidence that Mike has a mole within the DEA? I predicted it being the white moustached guy pre-season, but am now swinging towards Gomey.
Brock was very wary of Walt when they met in (i think) episode 3, and we never saw how Walt managed to administer the poison to the kid at the end of season 4. Walt's apparent confidence suggests he at least doesn't think the kid can blow his cover, but it's not too much of a stretch to imagine that Brock may recall seeing Walt sneaking away from his house or school at some point.
I'd be very surprised if the coughing and false identity in the precursor scene at the start of the season were not both red herrings. And I'd be amazed if the machine gun is to be used to kill anyone, it really isn't Walt's style.
The ginger kid in the pest control team who's been given a few speaking parts may have some sort of connection to a rival supplier. It's been established that these guys are all at least petty criminals, and the way this kid stepped up to ingratiate himself with Walt and Jesse suggests he either wants to become involved with them, or he wants to dig for info. I don't buy that he could be an undercover cop, that seems too much of a leap as until now the pest control team have only been involved in burglary.
Overall not entirely convinced by the rapid evolution of Scarface Walt, but I think Jesse's development as a streetwise, thinking criminal is both impressive and believable. I see Jesse as much more of a threat to Walt's long term control of the empire than Mike.
Sorry for long post, I've avoided the thread for a month and have jumped right back into it. Love this show