Here's an example of a mistake I made tagging to illustrate how I'm now thinking about tags. I originally created the following three tags for my team system nuggets: Visual Studio 2005, Team System, and Team Foundation Server. I did this because I first did my research on Visual Studio Team System tags and found that's what Technorati was using. I figured by covering my bases, users would find what they might otherwise miss.
The problem with this approach is I no longer had a single big bucket to show me all Visual Studio Team System posts. This approach is also error prone (tag a post with two out of the three buckets). Worse, I was cluttering my tag cloud, without adding value.
I then adopted the approach of thinking in big buckets first. For now, all my team system related posts will go into my Visual Studio Team System tag. If I need to chunk that up, then I'll add a tag for my team foundation server posts. If I need to further divide then I'll add tags for sub-buckets like source control, reporting, work items ... etc. I'll also draw from my research on Visual Studio Team System tags.
I should point out that while now I think in terms of big buckets to small, I like the fact that I can also jump right to the smaller bucket. However, I also know that I can count on one big bucket to contain all my smaller buckets.