I'm reviving this. Hoo-hah!
Okay, so here's the situation I'm currently in:
leak contains just under 1,000 questions and has the following excerpt:
A memory leak occurs when a program consumes memory that is not or cannot be later released to the operating system.
memory-leak has just over 7,000 questions and has this excerpt:
A memory leak occurs when a program fails to release memory that it has allocated but is no longer using and is not recoverable.
I'm a 10k user who knows absolutely nothing about dealing with memory leaks, however it doesn't take a genius to work out that these tags are used for the same purpose. I feel this particular example would be a guaranteed Synonymizer badge.
Now lets analyze the reasons why this was status-declined by @ShogDYIN':
If you don't have 5 votes in the tag, what makes you qualified to synonymize it?
I'm fairly sure the majority of tag synonyms were created out of common sense more than anything else. My example above demonstrates this rather well. You don't need to know the ins and outs of a tag to know that it has an almost identical wiki and excerpt to another one, and the questions in each are very similar.
...synonyms aren't a substitute for re-tagging improperly tagged questions...
As much as I'd love to spend my time editing countless questions to correctly tag them, I do have better things to do with my time. This reasoning is great when applied to tags which have 5 or 6 questions, but it takes a fair bit of time to go through 30+, especially on a slow internet connection.
I'm declining this because I don't think reputation - at least, not any reasonably low reputation - is a useful gateway here.
I'm going to quote here what @ShogDYIN' commented on his answer: "Hey, I have 80-something votes in the java tag, a language I haven't used seriously since Clinton was president. No system is perfect."
The existing system isn't perfect, but preventing somewhat high-rep users from proposing Synonyms seems silly. This is a bit of a lousy reason to decline this suggestion.
The important word in this discussion is suggest. Regular users don't outright claim a new tag synonym and have everyone else bowing down at their feet. Users suggest the creation of a tag synonym, and this is then voted on by others. In order to be approved it needs to receive a score of +4, whereas it only needs a score of -2 to be rejected.
When you consider that at 2,000 reputation anyone can edit anyone else's posts, requiring both 2,500 reputation and a score of at least 5 in that particular tag seems very overkill.
I'd like to see some more discussion going on here as I feel this was declined without good enough reason.
Update: Oh look, StackOverflow features tags pie and pie-chart, but I can't do anything about it, oh no.