AFTER ARRIVING AT THE GATE IN CHICAGO, FUMES & SMOKE WERE NOTED IN ZONE C OF THE CABIN, THEN THE CABIN LGTG WENT OUT & THE EMERG LGTG CAME ON. MAINT PSNL FND THE #2 APU HAD AN AUTO-SHUTDOWN DUE TO A MALFUNCTION. THE APU WAS PLACARDED AS INOP & THE ACFT WAS RTRND TO SVC. AS IT WAS CLBG, SHORTLY AFTER TAKEOFF, SMOKE BCM NOTICEABLE & THE CREW ELECTED TO RTRNTO THE ARPT & LND. AFTER LNDG, THE SMOKE HAD DISSIPATED & FIRE DEPT PSNL RPRTD NO INDCN OF SMOKE OR FIRE. SUSPECTING ONLY AN AIR CONDITIONING PROBLEM, THE CREW ELECTED TO CONT TO THE GATE. AS THEY BGN TAXIING, A FLT ATTENDANT RPRTD THE SMOKE WAS INCREASING, SO THE CAPT STOPPED THE ACFT & DIRECTED AN EVACUATION. A X-WIND PREVENTED PROPER DEPLOYMENT OF THESLIDES ON THE RGT SIDE OF THE ACFT. DRG THE EVACUATION, AN ELDERLY PAX, USING SLIDE L-4 ON THE LEFT SIDE, WAS SERIOUSLY INJURED BY OTHERS WHO CAME DOWN THE SLIDE AFTER HIM. ALSO, 5 PAX RECEIVED MINOR INJURIES DRG EVACUATION. AN INV REVEALEDTHE SMOKE WAS CAUSED BY OIL FROM A FAILED APU BEARING WHICH LEAKED INTO THE AIR CONDITIONING SYS.