The entire concept of "the upload", and all the reasons for and against, are predicated on the assumption that it's possible- Massimo Pigliucci, a brilliant evolutionary biologist turned philosopher of science who blogs and produces a podcast in his spare time, gives an example of why it may not even be theoretically possible.
To sum up his reasoning, the idea is that while we can simulate a cell that contains chlorophyll, we couldn't get a real sugar molecule out of it by shining simulated sun on it, meaning that there would be a permanent disconnect between reality and our simulation. Because of this, it is completely possible that the idea is impossible, even in theory. I'm not entirely sold on this- I take the stance that we could simply simulate the sugar molecule and all the secondary and tertiary effects, etc., until eventually we would be able to simulate everything relevant to the human brain, but that objection is made as a layman, and possibly a complete idiot. In any case, almost everyone agrees that simulating a human brain will probably be much more complex than just simulating the structure of our neurons, and could take hundreds of years. So, here's hoping that achievement will take place within the lifetime of my readership.
In any event, even if it's completely ridiculous, it is still a good exercise in critical thinking, so let's look at the cons.
First, we have to accept that even with "immortality," we will never escape death. Eventually, the last electron will decay, leaving us without electricity. But that's 10^26 years or so away. Even if we rely on some process independent of electricity, there won't be any energy left after 10^42 years. The odds are, our servers, wherever they were located, would be consumed in some sort of cosmic accident. But that's likely hundreds or even thousands of years after the upload- and I'd take the trade-off.
Second, we would die normally anyway. We couldn't transfer our consciousness into something other than our brains- we might be able to map the entire brain down to it's essential building blocks, and make a digital copy in some way, but the original brain would still be subject to the experience of death and decay. We would ultimately experience a normal death- but there would be another copy of us with all of our memories and personality intact. Again, I'd take this risk if it meant there was another me that was capable of watching my grandchildren's grandchildren grow up (perhaps inhabiting a robot body to play with them, or at least teaching them chess over the internet).
Third, what kind of life would it be? Great, I find myself in an ill-matched computer "body" with urges that can't be directly satisfied- what if I want a sandwich, for instance? Would I be living in an eternal dream like state "inside my mind", where my brain merely simulates everything with limited input from the outside world? Or would I be in some hellish prison of my own design, unable to indulge in any of the pleasures and rituals that make me human? This is the first con to give me pause- I'd hope that my download had been thoroughly tested and we were certain that it wouldn't drive us insane before I went in. But I still think I'd go for it- for me, even an eternity in torture is a plus over nothingness. And if it got too bad, I could (hopefully) beg someone to pull the plug.
Fourth, identity theft could be literal. We would be much more subject to kidnapping, and even worse, illegal copying/hacking. This is a terrifying consideration, but hopefully, the danger could be mitigated via relatively simple and cheap protection methods. Norton Anti-Virus for the soul, as it were.
Now, the pros are pretty simple. First, virtual immortality. Not only would we (or our copies, at least) avoid the unpleasantness of dying, they would never age. We wouldn't require food, at least not in the normal sense, as olfaction would be entirely simulated and possibly quite rewarding in its own right- many people I've spoken to consider fine food a great reason to pursue the endeavor of life. Think of it, not only the wisdom of the ancients could be passed down, as it is today, the giants whose shoulders we stand upon, the Albert Einsteins of tomorrow, could themselves preserved indefinitely, keeping us in touch with history in a way impossible now.
This leads to a second pro- no overpopulation. Real estate requirements would be minimal, food requirements would be non-existent. We would require some energy, probably quite a bit, but not much more than a battery of street lamps. Assuming energy continues getting cheaper, this would become more and more negligible as the years wore on.
Third, imagine the ways we could explore the universe! Without these fleshy bodies, we could travel between the stars, no longer requiring oxygen, no longer dependent on something as fragile as the human form. We would have none of the ethical concerns of sending generations of people to explore worlds far from our own- we could simply sign up for the mission.
Obviously, there are many more pros and cons, but I think these are among the most compelling and daunting, respectively. I hope this has given you food for thought.