I've been very lucky job wise; I've survived the job slump in the Boston, MA, USA area unscathed.
But I've kept my ears open.
There was a good "Connection" (PBS radio talk show) discussing this; the expert basically came out against spamming.
Better to send one or two resumes, custom tailored to the specific opportunity, that will stand out.
In other words, do the research on the employer and opportunity and juggle your resume to jump out at them.
Of course, I've changed jobs only twice in eleven years so YMMV.