Played a game last night where someone used an extremely effective, but also extremely cheap and lame tactic. The map was Bast, and in the Tram Tunnel outside Feedwater there is a vent in the ceiling.
For a skulk, it provides a fast route to the Engine Room area. A few minutes into the game I ran up into the vent only to discover it had been blocked by a Command Chair, and the marines were quickly building a TF and siege cannon behind it.
The skulks did their best to chomp through it and attack the other end of the vent, but they started sieging Feedwater before we could do much damage, and that was the end of the game.
Obviously there are very good reasons why CCs can be placed anywhere and can take a huge amount of damage, but using them as barriers just seems so.... wrong.