Is a double really unsuitable for money?

Very, very unsuitable. Use decimal.

double x = 3.65, y = 0.05, z = 3.7;
Console.WriteLine((x + y) == z); // false

(example from Jon's page here - recommended reading ;-p)

You will get odd errors effectively caused by rounding. In addition, comparisons with exact values are extremely tricky - you usually need to apply some sort of epsilon to check for the actual value being "near" a particular one.

Here's a concrete example:

using System;

class Test
{
    static void Main()
    {
        double x = 0.1;
        double y = x + x + x;
        Console.WriteLine(y == 0.3); // Prints False
    }
}