I've never done it, but I'm kind of hoping to.
I wouldn't listen to all the people who say "Definitely not; never get back with an ex!" At the same time, I would advise you to proceed with caution and consider the following questions:
Why did you break up? If one of you cheated on the other, how can you be sure you'll ever quite trust each other again? If you simply fell out of love, why? Do you think the flame has been re-kindled somehow? Or are you simply looking to go back for some comfort and security? Did one of you treat the other badly? If so, how do you know it wouldn't happen again?
What were the good and bad points of your relationship? You've both changed since you broke up; that much is inevitable. Would the good points still be relevant? Would the bad points still be the same, or have you both changed for the better? What did you argue about when you were together? Would the same arguments still be points of contention?
It's very easy to look back on an old relationship through rosy specs and remember only the good things. However, you need to ask yourself whether you're being realistic. If you get back together and then suddenly all the bad things come back to haunt you, you'll split up again and the memories of the second relationship will taint the memories of the first one. If it's unlikely to work a second time, perhaps it would be preferable to leave it in the past, so you always have fond memories of the first relationship. If you can look back on the first relationship and it brings a smile to your face, you need to think carefully about whether you want to risk tainting those good memories. On the other hand, if the first relationship didn't bring a smile to your face, you wouldn't be considering getting back together. Some couples get back together and the second time it works, so don't decide not to get back together purely to preserve the memories of the first relationship, if it means you're denying yourself the pleasures of a second, fulfilling relationship.
I would also advise you not to try and pick up where you left off. Where you left off is the point at which your relationship failed last time. I think to a certain extent, when you get back together with someone, you need to make a conscious effort to start from the beginning. This might seem difficult, but if you just fall back into old (bad) habits, the relationship is doomed before it even starts.
If you do get back together, think about what worked last time, and what didn't work. Everyone makes mistakes in every relationship. Don't let yourself make the same ones again.
Think very carefully about what you want to do, and good luck xx