I like both of Monda's schemes. I feel like in the long run I'd rather use the first, but the second one feels more modern and perhaps, like BoB says, more tempting to register at (that would only apply if it was set as the default skin, of course).

Transparency is not a problem - I'm not sure which IE versions support it, if any, but in either case it's a browser question rather than one of vB version.

That sort of gradient could pose more of a problem. If the blue page background wasn't also a gradient it could be cleverly worked around, but as it is, any workaround I can think of would be very clumsy.