I'm not 100% sure on what you're talking about, if you are just making it so you'd have to click on the "merged forum" to get to seperate forum sections, I'd vote no...*
However, if you're merging things like UMS showcase and Melee showcase (or whatever merges would be logical), I'd be slightly for it.
However, if and when starcraft 2 comes out, I'd say throw all the sc1 forums into a sc1 subforum to make way for sc2 forums
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* Edit: Well, actually, throwing map showcase + production into a subforum, I guess it wouldn't be that bad. Hopefully the script will be flexiable to allow us to easily rearrange things on demand?