Just played a Terran in 1v1 (I'm Protoss). He did a fairly common Banshee opening, I'd scouted it so it ended up being useless. I got an expansion up pretty early, saw he was going into Tank, Marine, Medivac so I got some Immortals, Blink Stalkers and teched towards High Templar.
He turtled in his base and built so many turrets and siege tanks to prevent me from getting in at all, especially seemed to want my observers out of there as he scanned every one that got near, so my game was basically to deny him expanding further than his natural and eventually he'll be mined out. I knew he couldn't expand so I just waited him out. I did suspect something was up as he so clearly didn't want me to see what was going on in there, but I just couldn't envisage anything he could do would be able to give him the upper hand.
Suddenly there were 10 Battlecruisers in my base, and I realised I've actually never had to play against Battlecruisers on ladder, and as such have never had to try to counter them. I assumed my Blink Stalkers and feedback from Templars would clean them up, but I was completely wrong. The feedback was helpful, but nothing else seemed to take their health down much at all. He ended up getting enough time to expand twice and continued to pump them out from 4 Starports, building no ground units at all for the second half of the game. In hindsight I probably should've switched to Void Rays, but I had no air upgrades, 3/3/3 ground upgrades and he did enough damage with his first Battlecruiser attack to damage my economy too much for me to switch from my 15 gateways to a load of Stargates.
So all I have to say is: why on earth are Battlecruisers so rare? They were an absolute nightmare to deal with and ended up losing me a game I was so on top of. The element of surprise of course played it's part, but for me to lose most of my army so convincingly against one of inferior supply, there has to be something there, right?