Oh well just to add, I can easily (and very often do) download at the same time as 1 or more of the 3 PC's in my house browse/IM/download themselves on my MWeb uncapped. Where do you get the idea that you can't do anything at the same time while downloading.. surely you at least mean everything else would be slowed down? I suppose you were only on 384, which alone on any ISP isn't great for families if you're downloading as well, simply because it's 384kb. The OP is asking about 4mb so I don't think your post applies.
And hey I can still max my line on filehosts any night, DL torrents etc.. do everything except simple browsing.
But Id say Openweb Gold is a better idea if you want to pay the extra R200 or so for it. I also wouldn't get 384kb shaped uncapped, it's just too slow when you shape 384kb and try to share that between a few PCs.