I have a Panasonic GH1 which shoots beautiful HD footage (hacked to up the bitrate thanks to the forums at DVXUser) and have been getting into making short videos for my blog as well as some family stuff.
Just in case anyone else wanted to try this, I find it works fine. My mini has no upgrades -1GB ram, 160GB hard disk.
First I convert the AVCHD files using VoltaicHD (it takes hours, so I leave it running overnight), then imovie downsamples (correct term?) everything while you edit, so there is no problem seeing what you're doing.
Obviously HD video editing on a little computer like this isn't ideal but if you're like me and love a very mobile setup, this works well.