I guess I can chime in here regarding the day-to-day work. I didn't work at a big firm, but I imagine it's about the same in terms of prosecution.
I worked as a patent agent, so my former day-to-day might be different than for an attorney. As another disclaimer, what I'm about to say is my own experience and not intended to be representative of what others on this board do on a day-to-day basis.
The keyword for my work was multitasking as the work for me was pretty much juggling a bunch of cases that were at various stages of prosecution and that have various deadlines. From my recollection, my day-to-day was to make sure things got done by a certain deadline. Each "thing" was different. For one case, it might be preparing a response to a first office action. In another case, the "thing" to do might be a response to a restriction requirement. And perhaps in another case, the "thing" to do might be a response to final office action. I also had foreign cases, so I might have to prepare a response to a foreign office action, get the response to the boss for review, back to me and to the mail room for faxing to the foreign associate. There's also drafting new applications sprinkled in there that take up a bit more time and research and maybe some due diligence here and there to break up the monotony of preparing responses.
If you're wondering what you do all day, you're pretty much stuck behind a desk, reading and writing and trying to figure out what witty thing you can say in response to an examiner. Some people say that they want to get into prosecution because you get to learn a bunch of different technologies. This is true, but don't expect to be sitting around reading and learning the technology for your pleasure. You have to keep in mind that you are billing your time out to a client, so you can't bill hours upon hours for "doing research" or "learning the background". I'm sure the client will not be too happy and it's likely that your boss will cut your hours if you spend too much time doing a particular task. Eventually, you get the hang of it, but once you do, you find you just learn enough to get something done. Sometimes you even wish that a case that you get is a technology you already know something about. Otherwise, you spend too much time trying to figure things out while there's other stuff on your plate to do. And for some strange reason, all the responses are due around the same time.
Also, one last thing about long hours. I used to put in long hours for research (in the lab) back in the day when I did research, and personally I feel those long hours are very different than the long hours during which you're stuck behind a desk, reading and writing and trying to figure out something good to say to an examiner, especially with a deadline looming over your head.