One more thing I’ve been thinking about are Tags and Categories. What is the real difference between these two concepts? Let me explain my own point of view on this issue.
Category is tree-like structure. I do have category “Ideas” here. I could create two subcategories - “Look&Feel” and “Client handling”. Then I would post everything related to blog view for end users to “Look&Feel” and my ideas on code implementing client I/O to “Client handling”. Still all such posts would be “Ideas”. Now, imagine I have found a very bad bug in my client handling code. The good place to post such info would be category “Bugs”, or better “Bugs”->”Client handling”. You see the bad thing here? We have to categories named the same with absolutely different content. Doesn’t look good.
At this point we shift to tags. Tag is just a label you can attach to your post. So you can mark is as “Look&Feel” and “Ideas” which would mean it’s a post about some design idea. Key point is an ability to make multi-tag requests. If you’re using Last.fm you might already noticed that there’s no such feature as querying a band that plays metal and does have female vocalist. Still you can filter bands by one of these tags. Bad implementation (there’s multi-tag search in last.fm playground btw).
Another one critical feature of tagging is an ability for author to see the list of tags and choose from them. Simple line edit with “type the tags separated by comma” trick doesn’t work. You might notice that there are tags “coding” and “programming” on my personal blog. I’ve been thinking of the same thing, but used two different words resulting in more tags with less elements. Again, bad thing.
Speaking about WordPress you can use categories and tags in the same time. The strange point here is that you can select multiple categories thus completely emulating tags with them, so you have redundant feature. This also looks like bad design.
I’m thinking of implementing only tags. This is more flexible way of storing items with similar content. And you can meta-tag with this feature too (see how project tags are resolved on about:farcaller).