When getting a macro lens, pay close attention to the ratio given. I know it's the case with film (which is what I shoot, lol i'm crazy and still in love with playing in the chemicals) so I'd assume so with digital. :] i. e. if you were to shoot a penny with a 1:1 macro lens, you would end up with a negative where the penny was the actual size on the negative as it is in real life. A 1:2 is half the size, etc etc.
I can't remember where the cutoff is for when a macro lens becomes silly and rather pointless, but as close to 1:1 as you can get! :] Macro=<3
And- you can always swap lens, BUT it changes some settings. I can't remember, but it throws exposures off a little bit if you're going to go full-manual.