With the recent patch (1.3.3) Archons are now considered massive units. I was wondering what inherent pros and cons, apart from being immune to concussive shell, are conferred by the 'massive' label.
Massive units can crush the Protoss Sentry's Force Field effect.
Additionally, massive ground units can't be picked up by the Phoenix's gravity beam (thanks, Nick!)
'Massive' is also an armor type (like 'armored' and 'light') and two units (Voidrays and Corruptors) deal bonus damage to massive units.