I have done both for years in linkaGoGo. In linkaGoGo tags are just called keywords. So from a linkaGoGo perspective:
Keywords = Tags
I use folders to give a bookmark a location where I can quickly navigate. For example all my banking links are in the Finance folder. I do that because folders provide a quick way to navigate to something as long as you remember where you stored it. In that case the bookmark is only one or two clicks away.
That is if I remember where I stored it. If I don’t remember what folder I stored it in, I fall back to searching. When doing a search, the keywords come into play, you would type a keyword like ‘bank’ and all bookmarks tagged with that keyword will show up. Most of the time the bookmark I was looking for shows up.
Note the above scenario describes a situation where I know what bookmark I would like to use. If I don’t know what specific bookmark I want to use, for example when I’m researching a topic about XML, I would search on XML in linkaGoGo. Then from the result list I start surfing. Also I can try to find a folder called XML. In general I do know what folders I have on linkaGoGo.
In the example above I use the Folders to navigate to something, either a particular bookmark or a folder about a topic. I use the keywords, as a fallback mechanism, in a search. Which means typing, which in my case is most of the times slower then 2 mouse-clicks. If I had a mechanism to quickly navigate my keywords with my mouse then things would get interesting.
On other sites I have seen a number of solutions for navigation tags. I have seen a list of all tags. With 585 unique keywords for my bookmarks that is not handy. The variation on the list used by Flickr and Technorati is showing tags with more links in a larger font. Another option, I have seen is displaying the 20 Tags with the most bookmarks, which is not useful, as it needs to be complete list. I do like the del.icio.us approach where after clicking a tag and new list of tags appears which is based on the bookmarks for the main tag.
So basically the feature linkaGoGo is missing is a good keyword (tag) browser to navigate your keywords. linkaGoGo used to have one before the whole tag hype started, but was not implemented in such a way that it was useful, so removed it. So without touching the existing features will bring Keyword navigation to site. May I’ll experiment with some interactive development where I will make a first cut available to play with and then refine it on feedback. With the Keyword browser linkaGoGo can do both worlds and even go across between them. Within the context of Keyword look at available folders or within a Folder context look at the available tags.