I know a lot of people seem to think Aqua may be gone come Leopard, given it's 5 years old. However, the FACT is Apple cannot replace Aqua without updating ALL of their applications individually. There are certain standard widgets that every application uses, scrollbars, pull down menus, check boxes etc etc. These could be updated quite easily and every app on your system that uses these widgets would show the changes. The problem is a lot of apps use custom aqua widgets, these are not standard and have to be made specially, you'll see them in the resources folder inside each .app package. To just give you an example, look in the resources folder of iDVD, there literally dozens and dozens of custom aqua widgets and interface elements. This is pretty much the same for every app, Mail, Safari, iWork, QT.... If Apple wanted to replace aqua they'd have to completely re-do all these custom widgets for each of their applications, not to mention all the 3rd part developers who also use custom aqua widgets. On top of this, there's the whole Blue/Graphite thing, a lot of apps provide widgets for each style and this is coded into the application. Therefore, even if Apple wanted to replace Aqua, they couldn't. You'd still have bits of aqua scattered throughout your system, meaning things could look very very untidy.