I'm a designer, and I hate lorem ipsum. Let me tell you why. Firstly, mockups that use lipsum typically assume that all pieces of content will be filled with equal amounts of text. Typical lipsum mockups with equally-sized blocks of latin therefore give a free pass to designs that break with uneven or unusually large amounts of content (like vertically aligned columns). They also fail to uncover issues where narrow columns and textareas create 'rivers' of whitespace when words don't quite fit into the space. Secondly, using realistic text in wireframes is a great way to expose pieces of content that don't make sense in practice. Perhaps the content would be redundant, or would be difficult to fill in real-world scenarios. Either way, that's not something you want to discover at the late stages of the design process (or worse, post-release). You don't necessarily have to write your own copy - just pasting in something from another website with similar content will typically do. Thirdly, because lipsum is not to be read, it allows designers to forget about readability and text legibility in favour of shaping text sections to fit into their design. That's risky practice, and at worst it creates unusable content and websites with text that looks pretty can't be consumed. And that's killer. Granted, sometimes there aren't any alternatives. Sourcing realistic content - even when it's copypasted from somewhere else - is a time-consuming exercise. But I'd always recommend trying it out before signing off a design, because the alternative is just too, too risky.