I, personally, don't see any conflict in this one. The Market Age uses Gmail to describe their little known research application service. Google uses Gmail to describe it's free mail service. I can't see anyone confusing the two, or signing up for Google because of The Market Age's reputation.
Different fields, simple abbreviation, no reason to believe Google is trying to profit off the other one for a grand total of no conflict and thus no case. These guys are just trying to get some free publicity and rattle some sabers so they protect their trademark. That doesn't mean Google can't use it too. Google may even pay them a little bittle of cash to sign something agreeing that there's no conflict, just to shut them up (whether the case has any merit or not becomes secondary when Google has an IPO coming up), but if it comes to a fight, Google will crush them.
With the usual disclaimer that I'm speculating about the outcome and don't have actual psychic powers and that I'm not a lawyer and don't play one on TV.