Many people use Adobe Illustrator or Photoshop for designing Web layouts, but a lot of companies use Visio – especially for higer level ‘wireframes’. One of Visio’s problems (<= 2003 anyway) is that it doesn’t support pixel units. This means you’ll always be approximating the sizes of content areas and page elements, making the developer’s job more difficult.
Enter ‘Visio Guy’, and the Pixel Unit Line Shape. This is just a great addition for anyone using Visio. Before you know it you’ll be laying out pixel perfect shapes that the developers will then give you great pleasure in declaring ‘this won’t work in IE6!’ 🙂
A thing to note with Visio as well: If you’re working with pretty small dimensions then the only way to get really precise is to zoom right in (like 500%), otherwise the whole ‘snap/glue’ thing will kick in based on the page units (probably mm), regardless of whether you’ve switched snap/glue off.