Capital and class
Some thoughts on these matters...
Capital
To be a capitalist you need to have capital it is not enough to mearly think you are a capitalist. In fact most members of the proletariat probably consider themselves to be capitalist but they are obviously not capitalists — the relations of production determine which class people belong to not their consciousness.
Class
The terms working class and middle class generally seem to be used in the UK in a non-Marxist sociological way, this can be quite divisive, especally when compared to the Marxist concept of working class, which does include the petite bourgeoisie and the lumpenproletariat (though this term is no so useful these days...).
The term proletariat (and the corresponding ruling class, the bourgeoisie) is probably far more useful since it doesn't have the cultural connotations that working class and middle class have.
Most people that are probably generally considered to be middle class in the UK are actually members of the proletariat — the class someone belongs to isn't determined by their consciousness, the proletariat generally has a bourgeois consciousness — the dominant ideas and beliefs in society are those of the ruling class.
The mode of production
The capitalist mode of production has superceded all others and now dominates the planet, though, for the first time since the dawn of capital a new mode of production is emerging, the mode of production of Free software (see also Free software).
Practical applications
See this email to the Matilda list.
See also
A good starting point for reading more about this is still the Manifesto of the Communist Party, bear in mind that this was written as a call out — there was no communist party when this was written...
Also, of course, Das Kapital Marx and Engles' Kritic der Politischen Oekonomie.
Free Software and Market Relations and Free Software & GPL Society are good introductions to the Free software mode of production.