As many people have pointed out the Steam Tank is a lightning rod for controversy.
When I first got back into the game for 6th edition, I immeadiately got into a campaign with some vastly more experienced players.
I used the Steam Tank and two units of 8 HC. They told me up front that this would be considered very poor form in any other environment. However, we were playing a very strict comp version of the territorries campaign and I was able to fit it in my list. As we were unable to alter our list it stuck and people just didn't say anything.
I ended up winning every game I played. I became very good at using the ST. I would deploy it center and then do a double envelopment with the knights. It was basically unstoppable against these very comp heavy armies.
I have stopped playing with it, because A) I am much more experienced and don't want people blaming my win on one model, B) people that don't know you will HATE the model, and C) gamers that don't play against it will not believe how it breaks nearly every rule in the game and will be additionally pissed off by it. Which will also entail you digging out the 2002 annual and letting them read the whole article, and you might as well let them read the errata as well.
While it does see a lot of play at comp less tournaments it is almost universally despised by everyone that doesn't use it, and using it at an RTT almost gaurantees you won't win any awards as your sportsmanship scores will, most likely, get trashed by anyone you beat.
Like many hard models skill is a huge variable. In the hands of a novice it is a pain in the neck but not insurmountable, but in the hands of an experienced player it does give off the odor of cheese.
It is hard to know what is right when selecting a model like the ST. Many may make the argument that the empire needs a leg up with all the monsters, chariots and rock hard lists out there. Others will say that the model doesn't belong in the game at all, from both a fluff and game mechanics perspective.
However, it can be hellishly effective, if you learn how to use it. You can change someones entire deployment with it. It may be 300+/- points but it will hold and often roll a flank all by itself, and in my "Damn the Torpedoes, Full steam ahead" method it will disrupt an entire battle line.
Don't forget to pop the engineer up and take his free shots. You would be surprised at how effective he is with a repeater pistol.
And stay away from dryads, they can tear the ST apart. Trust me, I know.
-Joseph