Jakob Neilsen has written about the 10 best application UIs of 2008. And NZ-made Xero comes in at #10! First of all, congratulations to Xero, the Team and Rod Drury!
Neilsen is recognized as one of the leading usability, analysis and UI design experts in the world. So his recognition of Xero, from little old NZ, is significant. He went one step further and used Xero as an example of how to implement lightboxes / modal dialogues well. He also gave Xero extra kudos for the emotional design, given that Xero targets a traditionally 'dry' audience:
But Xero might be a more interesting example, simply because it targets the traditionally dry domain of accounting. One of its main features lets users automatically reconcile bookkeeping entries with bank account transactions. As a match is made, the 2 matching entries are removed from the list of stuff to be reconciled. Users compared this interaction to playing Tetris and described it as fun and addictive. Come on, making accounting fun? That's an award-winning design.
(Emphasis is mine).
Disclaimer: I use Xero, enjoy it and find it extremely valuable. I recomend it to NZ freelancers and home, small and even medium businesses. I am not affiliated with Xero in any other way.