There are a couple of problems with using the live multitasking vs homescreen widgets: 1. The live multitasking is less flexible. Neither the user nor the developer can choose the size of the 'tile' or where it is located. The latter could be an issue when there a large number of applications running.
2. The live multitasking view is non-interactive, so you can't replicate the features of a search widget or media widget, for example.
The point regarding the icon grid is that it's an inefficient method of finding your chosen application, once you have a large number installed. It should only be required as a last resort, for those applications that you don't often use. One of the complaints about the iPhone is that users have to frequently scroll through a long list of applications. Meego-Harmattan adopts a similar approach, and exacerbates the problem by omitting the option to save bookmarks within the browser application (at least in the version I'm using). If you have 50 web bookmarks plus a large number of applications, it's going to be a PITA.
These issues aren't dealbreakers, they just make the UX less flexible than what I prefer, but I'm happy with the general concept of swiping to minimise/close applications, because it works well. Marko Ahtisaari explains what I dislike about the UX in a single sentence: “I know we have out simplified the iPhone”.