It's been stable so far; autosave addition nice; Mail & Safari mods seem to parallel many of the non-Mac goods out there and are welcome additions; "mission control" as a broadly parallel replacement for spaces works well; "launch pad" universal app/program launcher also nice but not really a big step (for me) from an applications window or a spotlight search window. Swipe movements work well, though the "native" scrolling mouse motion reversal is taking me some time to get used to. Keystroke shortcuts seem to all be working, but I've not been methodical about it. I think it'll probably interface well with the cloud, and the modifications of the app store that are coming. Like snow leopard, I suspect Lion will be a required upgrade for future IOS and OS roll outs, though apparently IOS will eventually replace desktop/laptop OS...So far, so good!!