I know I'm in the minority here on this one, but I actually wish iTunes Match would leave my Apple Lossless tracks LOSSLESS...I don't like them being converted to AAC @ 256. Sure there isn't an audible difference in most cases but I'm a lossless guy and wish they would allow for that.
I have a fair amount of lossless my self - but it is no problem. iTunes match will leave them in their original format on your HD if they are > 256 kbps bit rate, it is only the upload that is transcoded to 256 AAC. Best of both worlds - lossless for your local network for home music, more manageable (but much smaller) 256 files for streaming to devices on the go.