OpenELEC – just another embedded Linux distribution to build HTPC, recently was lunched in version 1.0. It uses XBMC as a front-end and customized back-end. OpenELEC is designed for Intel-based, Nvidia ION-based and AMD Fusion-based systems and run from USB stick or memory card. Special build will be available for Xtreamer Ultra platform (Xtreamer is a partner of OpenELEC). The size of ISO is just about 100MB (depends of the platform type) and it requires less than 130MB on the HDD.
Except a small size and nettop application OpenELEC offers a very simple way for configuration, extending by add-ons (such PVR for LiveTV, Torrent clients, rsync, LCD/VFD display support), an open add-on framework, GPU acceleration (Intel VAAPI, nVidia VDPAU, AMD XVBA (via VAAPI), Broadcom CrystalHD).
So, get OpenELEC 1.0 ISO, make bootable USB and try new HTPC software.