One of the questions you'll have to ask yourself is this: will these achievements be rewarding current behavior or be used as incentives to increase specific behavior?
For example, one of the websites I built and help run allows users the ability to earn "badges". These achievements are based on measurable activities that anyone can achieve based on their participation. We have a badge for having 10 or more discussion posts, and then 50 or more discussion posts. We also have a badge for the 10,00th user.
So there are badges for multiple purpose the primary function, for us, is to increase traffic and user participation. I think this would be a great idea for an intranet where participation is crucial to keeping content current, and encourage collaboration.
I'm also an intranet architect/admin (SharePoint 2010), so here's a couple of my ideas of what metrics might be useful to measure achievements within an intranet:
- Number of Comments posted
- Number of Discussion Thread started
- Number of Documents Uploaded
- Number of Times a Person used the searched
- Visited more than X number of areas
- Voting based achievement (users can vote for the person who will get a specific achievement or award)
These metrics have to be easily measurable within your architecture. It's hard sometimes to try and capture how many times people searched; there may not even be a way to record that metric. As you can see, most of my examples are based on an achievable goal, such as a number. In some cases, you might just want to hand out a "special achievement" that's not based on any metric; rather arbitrarily. For example, sometimes we pass around the "dog of shame" badge to others within our website just because we can and it spurs conversation and wonderment with our customers. It's quite the popular badge.
Some achievements may push your users to compromise the credibility of your achievements. For example, lets say that you use the "Uploaded more than 100 Documents" achievement. The original purpose for creating that achievement was to reward users who are sharing the most information by uploading it. There will always be that 1 guy, you know the type, that will upload hundreds of useless documents that may not even be relevant. He'll earn the achievement, but he earned it in a less than ideal way, which decreases the credibility of the achievement. Achievements are best valued when they have credibility and prestige supporting them. So achievements should not be easily gamed, or at least, highly monitored to prevent this situation.
You'll have to really put some thought behind achievements and the desired results that stems from the behavior they encourage. I hope this helps.