I heard the ATIS at San Carlos (SQL) "1100 scattered," got
clearance from the tower, and departed on runway
30 for a right downwind in a rented 172.  At 700 feet I 
could see I was about to enter some clouds unless I started 
a hard climb, so I pitched for Vx, and started my crosswind 
and downwind turns.  The tower told me to switch to Bay
Approach.  As I was switching the radio and continuing to
climb, I realized I was headed into the path of a 727 landing
at SFO.  I was at 2000 feet and had busted SFO "B" airspace.
  I started a right turn and rapid descent out of the "B."
I contacted approach, and they asked "are you the aircraft
that just entered Bravo over SQL without a clearance?"  I
said that I probably was, and was told to call a phone
number on the ground.  
  The rest of the flight was uneventful, and when I spoke to 
the ATC supervisor, I confessed, explained my attempt to
remain clear of clouds, and we talked about how the better
thing to do would have been getting a Special VFR and 
departing on the downwind at TPA (800 feet).  He was
polite and understanding, and helped me learn a valuable
lesson, that "scattered" clouds aren't scattered if you
fly right into them.  Fortunately he accepted my safety
decision and did not ask for any of my license information. 
As a 100 hour pilot, I had not learned to judge clouds 
accurately.