Numbers still maintains its slightly strange way of dealing with spreadsheets. Unlike Excel, which remains fundamentally an out-and-out number crunching program, in Numbers tables are dragged onto the workspace and can then be related in various ways.
When it comes to powering through maths, both methods have their advantages and there's nothing wrong about either, but for the casual user I think Numbers has the advantage.
That's an opinion reinforced by the improvements made to formula writing in Numbers '09. The Formula Browser, features some 250 functions, all with excellent explanatory text and some even offering embedable examples. This allows for easy creation of complex spreadsheets, although most users should find a pre-made template to cover their needs anyway.
Formula list view could well prove useful, oddly enough showing a list of every formula used in each spreadsheet. These can be searched through and there's a find and replace option, too. Also added are table categories, enabling quick grouping of similar data into collapsible sets.
Linked charts, a stalwart of Office, make a showing, meaning tables and graphs embedded into Pages, Numbers or Keynote documents can be updated as and when needed from Numbers, with the change showing in any document that spreadsheet is embedded into.
Unsurprisingly for a Mac-centric program, Numbers '09 boasts more whizz-bang 2D and 3D charts that you could shake a large stick at. Mixed charts are a great addition, allowing multiple data series to be displayed on the same graph for easy comparison; say your 2008 to 2009 profit predictions, versus the actual results. Trend lines and error bars can be also be added and, of course, there are myriad options for making said graphs look pretty.