I was thinking about it, however I've found that String performance is horrible (at least with Japanese strings) if you do anything like hasSuffix() or hasPrefix(). I think the problem is that String converts to unicode code points as soon as it seems useful, instead of keeping everything in UTF-8 (or whatever, really) and doing memcmp for hasSuffix() and hasPrefix() specifically, which would work much faster. Using NSString everywhere is faster, but then string concatenation involves a bunch of casting.

I'm not much of a server guy, so I might be wrong here, but dealing with strings seems like something a server is likely to need to deal with. Although, maybe the strings are short enough that it's not much of a problem, or maybe strings that are almost always ASCII are fast. Anyway, something to keep in mind.