C182 pilot experienced airborne conflicts both arriving and departing SQL near IMPLY intersection. The departure incident was a NMAC with no evasive action taken.

Narrative

While inbound to SQL; after passing SUNOL and heading toward Coyote Hills; when approximately at IMPLY; I noticed opposite direction traffic at my altitude on a collision course. I made a 90 degree turn to avoid the traffic. The other aircraft (a C172) did not change direction. I believe the other pilot never saw me. We probably passed within 200 feet of one another. The same day while outbound from SQL and in approximately the same location; while climbing through 2500 FT; I was passed directly over head by a Cirrus. Separation was less than 200 FT. The place where these incidents happened has a high concentration of traffic inbound and outbound from both SQL and PAO because of a gap between the hills and because it is below the Bravo airspace. I believe that these incidents are representative of a serious potential for a midair collision in this area. Also; since I experienced two such incidents in one day; close calls like this must be happening regularly to other pilots. Therefore; I recommend that the FAA issue a safety advisory to Bay Area pilots reminding them to exercise extreme caution in this area because of highly concentrated traffic. Furthermore; a landing light should be illuminated at all times (day and night) while between SUNOL and SQL or PAO.