Was curious as to the speed of floating point operations on the 16MHz Arduino Diecimila. Could only find a few threads about that (e.g., http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1206534749), with no answer, so I ran some tests. Here's a graph of results comparing the speed of a multiply operation using the various data types:

The way the C test program was set up, the values above include the time for the multiply operation as well as one memory read and one memory write.

These are the lengths of the data types in bytes:

byte 1 int 2 long int 4 double 4

I also looked at the time to do a sin() call to the math library: 255 microseconds!

Anyway, based on these results, looks like the Diecimila is about a 0.1 megaflop device, using 4-byte floats/doubles.