erm, pretty much everywhere. one example - you have a "free trial" button, but below that a required form field, swap them over, surely?
the free demo button doesn't work - goes to a page not found or sits there saying "building your site"
i feel like this "Making it easier to collect, collate and consolidate data and figures." is a really really poor description of what your product is. have you tested that it resonates?
i don't seem to be able to drag charts to move them, if i click the graph once it shows me formula, i click away to change view and it selects whichever cell i clicked in, i press cmd + z to undo and nothing happens.
everything feels like a lot of work, for example all the buttons need much much faster tool tips. why when i hover over one doesn't it tell me what that button is in the silver bar to the right?
why are some things formula and others lightbox ui controls (eg: add a link) feels like consistency for that stuff is ++
Site > Settings > Pages is honestly terrifying. draw some inspiration from Numbers.app? :)