Users can suggest tag synonyms and vote for these suggestions. When enough users vote the tag synonym is created. The whole system has some significant flaws:
Synonym suggestions have almost zero visibility. They're only visible on the synonym page of that tag (and a rather obscure list of suggested synonyms only available to mods).
The requirements to be able to even suggest tag synonyms are very high, you need at least 2500 reputation and at least an answer score of 5 in this specific tag.
Creating a tag synonym is not sufficient, the tags should also be merged. This requires a moderator anyway, and it is a sufficiently dangerous tool that likely will never be available to regular users.
With the exception of trivial synonyms like plural forms and similar cases, all non-trivial synonym suggestions should be discussed on meta anyway.
This might not apply to Stack Overflow, but my impression is that tag synonyms are almost never created via the suggestion route on SE 2.0 sites, but pretty much always directly by a moderator. The requirements to even suggest a synonym are just too high and the visibility of suggestions is so low that it is nearly impossible to get a synonym voted on often enough on SE 2.0 sites.
My suggestion is to remove the suggestion of synonyms entirely, at least from the SE 2.0 sites, maybe not from Stack Overflow (depending on how often it is actually used sucessfully there). All synonyms would be created by moderators after being proposed on meta.
For users that don't know how futile it is to try to suggest a tag this way the whole thing is just misdirection, they should be steered towards making a meta post about the synonym. This is almost always the better idea, and had a much higher visibility and more room to discuss the impact of the synonym. It also means that mods are aware of this and can just create the synonym and merge if a consensus emerges.
The one thing the suggestion route might be useful for are trivial synonyms, but I've no data on how often those are suggested via this route. I suspect that only SO has a high enough volume for this to be useful.
