First off, don't be intimidated about tanking. There's this weird thing, I've noticed, where people who aren't tanks make it out to be a lot harder than it is and are too scared to try it out because of the perceived pressure. It's not that bad. If I can do it, clumsy as I am, almost anybody can. Just read forums, watch videos...which it sounds like you are doing already...and you'll pick it up in no time.
About flashpoints - they aren't too bad, but in my experience at least I actually find the trash is a little bit trickier than the boss fights because a lot of DPS won't follow a consistent kill order. You can't expect to pick up EVERYTHING. I'm a PT, so I've got my Death From Above, Explosive Darts, Flame Sweep, a grapple, and a good Carbonize/Flamethrower combo going, and I STILL can't always get them all rounded up and staying on me. There are a lot of pulls with random weak and standard level enemies hanging off on the fringes. In a good group, the DPS will pick those off almost instantly at the beginning of the pull while you focus on keeping aggro on the strongs, elites, and champions. Sometimes the DPS by instinct will attack what you are attacking right off the bat, so you may want to gently remind them to go after the little guys first.
About operations - the biggest thing I have faced here is psychological. I tank for a small guild that has cleared most of the 55 HM content, and the one major responsibility that has hit me so far is my need to be available. In my experience when I cannot make a scheduled hard mode operation, the raid is off...but when a DPSer or healer cannot make it, the group will often find a replacement. I tend to be of the mindset that I am fully replaceable even by an alt of someone who knows the fights, but for better or for worse a strong reliance and dependency on a particular "main tank" seems to be ingrained in the minds of many MMO players. Regardless of whether you consider yourself a leader or not, you will most likely be looked to for leadership. That's another ingrained instinct I have run across.