It's good if you buy on ebay a lot.
But if not, then it's still good, but it is slightly weird. I don't know if things changed, but I believe you need to earn $5 or more in a 3? month period to get the bucks. Then after, they issue you it and that is applied to your account, but it is only valid for 1 month. Then your bucks expire. If you don't hit $5, you lose anything earned those 3 months and have to start over again the next period of 3 months.
So if you don't use ebay much, a lot of times you won't hit that $5 threshold and you lose it. It's no biggie honestly, since it is just extra incentive. It isn't like it costs anything to be in the program. It just sucks to see them vanish, and having to wait through these periods.
Again, I don't know the exact time frames and numbers that I mentioned, but I believe those were the terms in the past.