The main problem with the canonization process is that it typically takes more than a hundred years. There are exceptions of course (e.g., St. Francis of Assisi was canonized one year after his death, or St. Maximillian Kolbe was canonized very quickly--but in his case it was because Pope John Paul II wanted him canonized), but as a rule it takes so long that the person who starts the process is rarely the person who brings it to completion.
That is the main reason why most Catholic Saints are deceased members of one or the other religious order (i.e., monks, nuns, friars, etc): An order can afford to have a member who dedicates his/her life to working on the canonization of its members. A diocese rarely has such a luxury, especially in these days of fewer and fewer priests.
As for the miracles, the way I remember it, you need two for beatification, another two for canonization.
As a curiosity, I overheard during my years in Rome that Opus Dei had doctor-signed documents about miraculous healings caused by the intercession of their "deceased" founder while he was still alive. Nothing like being prepared! | 
