I think it's better than the alternatives (if you don't want to use condoms all the time) as it has no proven links to increasing the risk of cancer etc. However I will be getting mine removed in the New Year, 18mo early (implanted June 2010), as I've just had a heavy, fortnight-long period and have decided the positives no longer outweigh the negatives. The implanon has helped with period pain but I was led to expect them to stop entirely (have since read that this is only true in c.20% of cases) and if anything they've got longer.
I have gone from being a reasonably placid person to having bouts of uncontrollable rage (literally shaking and screaming inside - haven't felt like this since I was a very young girl and had fights with DSis) and picking fights with DP. For the first month or so after I had it put in I also had severe bouts of dizziness, which impeded my coursework (this is why I'm taking it out in the NY - I can't risk my work being impacted this term). I also cry at the drop of a hat now, when I never used to.
The other major reason I'm getting it removed is that my sex drive has dropped to almost zero. I'm only 24 and don't want to turn around in a few years and think I wasted the healthiest years of my life on going to bed early with a good book! 
OTOH, I experienced very little weight gain and have been able to lose what I gained. It is very convenient not to worry about pregnancy or the most serious side effects of other hormonal contraceptives (I would never go on the Pill for those reasons).
DP agrees with me getting it taken out and has suggested it on a couple of occasions. He looked relieved that I'd made a decision - I hadn't realised how much my mood swings were impacting on him. The sex thing doesn't bother him but the emotional side definitely does.