sorry beatfried, i totally missed that
mining --- e.g. bitcoin, litecoins, protoshares, etc.pp. --- means that you're searching values in a pre-defined calculation that meet certain characteristics (often it just means that the solution of a specific calculation needs to be less than a specified value, which is the current/fluctuating "difficulty").
these characteristics often contain a random property (e.g. using a hash function that needs to be calculated).
thus all the miners are doing is "just" a (VERY LARGE) trial-and-error on all possible values to find a value that meets the current target difficult of the network.
thus sometimes a block needs 1.000 shares, sometimes 1.000.000 shares.
- xolokram
ps. i hope that was helpful
pps. i'll redirect the old pts page (ptsweb.beeeeer.org) to the beta pages (beta.beeeeer.org) soon®