Apparently Microsoft Excel 2007 can’t do it’s times tables. Microsoft employee David Gainer, has posted on the Excel Blog that when computer users try to get Excel 2007 to multiply some numbers, and the result was 65535, Excel would incorrectly display 100000. Gainer said Excel makes mistakes multiplying 77.1 by 850, 10.2 by 6425 and 20.4 by 3212.5. Gainer said the bug is limited to six numbers from 65534.99999999995 to 65535, and six numbers from 65535.99999999995 to 65536.

Microsoft is currently trying to address this problem.

UPDATE
Microsoft has now addressed this problem with a patch
See the Blog entry Here