I know many people on LJ (including some folk on my flist) have been asking and asking for a tag merge feature. Well you need wait no longer - it was released yesterday.
This is what LJ had to say:
In this release, the Manage Tags page has been updated, and 2 new features have been added to it.
1) You can now merge tags. When you rename a tag to another tag name which already exists, it will combine these two tags into a single tag using the name you specify.
2) You can select up to 10 of your tags and enter new tag names to add to all entries which use one or more of those selected tags.
Of course as well as adding the feature they have totally changed the Manage Tags page to 'fit in' with the 'new' standard site scheme *sighs* I haven't used it yet, so I can't comment as to whether I think it's an improvement or not. However, the fact that all the tags no longer appear on one page is somewhat negative for me. OTOH, you can now search your tags, which is a good thing - so we'll see.
For those of you who have been waiting and hoping this feature would be appear - have fun!