A small question.
When someone has a Google PR 4 for example, what does the "4" mean?

Its a measure of how good the page is.. Relying on such things as back links..

Its a value between 1 and 10 with 10 as the highest

Hope this helps

--James

If you want your pagerank to increase, get more sites to link to you. However, it should be noted that higher ranks get increasingly harder to achieve.