This is a disaster.
I just downloaded two .xlsx Excel documents, and attempted to open them in the new (2013) Numbers.
These were the simplest possible documents. 101 rows, 17 colmns, no header/side labels. I don't think it included any calculations at all. My coworker used Excel simply to format her data as a table.
The imported Excel table is almost completely blank. A column of dates, and a couple of columns of literal numbers survived. It lost all of the text. I'm sure the column widths were lost. If you try to edit a cell, the editing bar at the bottom does nothing; it has no content, it does not respond to keys or clicks, it stays blank and unresponsive when you select a cell. If you type an = in a cell, there is no expression builder, and clicking in other cells to add them to a calculation merely changes the selection to those cells.
In iWork 2009, the apps posted a notice when they couldn't make a 100% faithful import — and in my usage, those were for missing fonts, not absent functionality. No such notice here.
Is there any way I can read at least a spreadsheet that makes no use of Excel features?
Further remark, but not a question
I had heard that the days were gone when people had to install Office because that's what they use at work. I managed to get away without using Office from 1989 to this day. I think it's ironic that at the moment Microsoft lost its lock on productivity tools, I am now forced to install Office.
I regret the testiness of my earlier posting.
I found the iWork '09 folder in my Time Machine backup, and pulled it back in. I didn't have to do anything about the system components — they were still installed.
When I opened the problem file in the old Numbers, I had the same problem. That eliminates Numbers 3.x from the equation.
I'm downloading the current NeoOffice (Java, sigh). I've filed a bug report rdar://15351913.
I'll mark this answered (I see someone else has posted while I wrote this, and I'm interested to see what he says.)