DEPARTING C182 FROM BFI REQUESTS AND OBTAINS VFR FLT FOLLOWING THAT SOMEHOW BECOMES CONFUSED.

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I WAS NWBOUND OUT OF BFI AT 2900 FT; UNDER THE SHELF OF SEA'S CLASS B (3000 FT FLOOR); ENRTE TO SKAGIT REGIONAL (BVS); A RTE I FLY VERY FREQUENTLY; ALMOST ALWAYS WITH FLT FOLLOWING (OR IFR; DEPENDING ON WX). I WAS 3-4 NM OUT OF BFI (ABOUT 8 DME FROM SEA) WHEN I CONTACTED SEA APCH AND REQUESTED AND WAS ACCEPTED FOR VFR RADAR ADVISORIES. AFTER CONFIRMING RADAR CONTACT; APCH ADVISED ME TO REMAIN CLR OF CLASS B AIRSPACE; AND I REMAINED LEVEL AT 2900 FT. I WAS HANDED OFF TO ZSE SOON AFTER THE SHELF WHERE THE CLASS B FLOOR RISES FROM 3000 FT TO 5000 FT (SEA 12 DME). WHEN CTR RESPONDED TO MY CHK-IN; THE CTLR ASKED MY INTENDED CRUISE ALT (4500 FT). SHE CLRED ME TO CLB THROUGH CLASS B AIRSPACE BUT ALSO SAID TO REMAIN AT 3000 FT. I DO NOT RECALL THE EXACT WORDING OF HER 3000 FT REQUEST -- WHETHER 'MAINTAIN 3000 FT' OR 'ADVISE OF CHANGE' OR OTHER TERMINOLOGY. FIRST PROB: SINCE I WAS ALREADY PAST THE 3000 FT CLASS B FLOOR; THE REQUEST TO MAINTAIN 3000 FT RENDERED MOOT BOTH MY CLB TO 4500 FT AND THE CLRNC TO ENTER CLASS B AIRSPACE. BUT HOLDING AT 3000 FT WASN'T A PROB (YET); SO THAT'S WHAT I DID. BUT THEN THE SECOND PROB AROSE. MY PLANNED RTE WAS OVER THE TOP OF PAE; WHOSE CLASS D AIRSPACE HAS A CEILING OF 3100 FT. AFTER A FEW MINS AT 3000 FT WITH NO FURTHER CONTACT FROM CTR; I WAS GETTING PRETTY CLOSE TO THE PAE CLASS D AIRSPACE; WITH NO CHANGE IN MY 3000 FT RESTR/REQUEST AND NO VERBALIZED CLRNC TO ENTER THE AIRSPACE. THE CTR CTLR WAS VERY BUSY AND I HAD DIFFICULTY SQUEEZING IN A CALL; AND WHEN I DID; THERE WAS NO RESPONSE. BY THEN I WAS 0.5 NM FROM CLASS D AIRSPACE. SO I INITIATED MY CLB TO 4500 FT. I REASONED THAT THE RESPONSIBILITY WAS MINE TO AVOID CLASS D AIRSPACE; HAVING NOT BEEN CLRED TO ENTER IT; AND THAT BECAUSE I WAS VFR AND IN CLASS E AIRSPACE; THE 3000 FT RESTR WAS A SUGGESTION AND NOT A REQUIREMENT. FURTHER; I AM FAMILIAR WITH PAE'S AIRSPACE; INST APCHS; AND HOLDING PATTERNS; AND I BELIEVED I COULD CLB SAFELY WITH GOOD VISUAL LOOKOUT (I ASKED MY PAX TO ALSO KEEP A SHARP EYE FOR OTHER ACFT). BUT OF COURSE THE CTLR COULD NOT KNOW OR COUNT ON MY FAMILIARITY. AS I WAS PASSING 4000 FT; THE CTLR CAME BACK (THE FIRST CONTACT IN SEVERAL MINS) AND ASKED WHAT ALT I WAS CLBING TO. I TOLD HER AND SHE HAD NO COMMENT; QUESTION; OR APPARENT CONCERN. I THINK 'ROGER' AND NOTHING ELSE. WHEN SHE PASSED ME OFF TO THE NEXT SECTOR (WHIDBEY APCH) A FEW MINS LATER; THAT CTLR ASKED ME TO CONFIRM MY ALT (LEVEL AT 4500 FT) AND INQUIRED WHETHER I WAS IFR OR VFR. AT THAT POINT; IT DAWNED ON ME THAT THE ZSE CTLR MIGHT HAVE BELIEVED I WAS IFR AND HANDED ME OFF TO WHIDBEY AS AN IFR FLT. AS I NOW UNDERSTAND THE FARS; THE INSTRUCTIONS TO MAINTAIN 3000 FT CONSTITUTED CLRNC THROUGH PAE'S CLASS D AIRSPACE. BUT I DIDN'T RECALL OR UNDERSTAND THAT AT THE TIME; AND I ERRED IN INITIATING MY CLB. HOWEVER; THE ENTIRE SIT WAS ATYPICAL. I FLY THE SAME RTE VERY FREQUENTLY; AND CLBING NORTHWARD OUT OF BFI WITH FLT FOLLOWING; THE USUAL ACCOMPANIMENT TO THE FIRST 'RADAR CONTACT' ACKNOWLEDGEMENT IS CLRNC TO CLB THROUGH CLASS B AIRSPACE; SUGGESTING THAT ATC USUALLY PREFERS TO GET TFC AS HIGH AS POSSIBLE OVER PAE. (PAE IS A BUSY GA ARPT AND HANDLES LOTS OF PRACTICE APCHS; AND AS THE SITE OF ONE OF BOEING'S MAJOR PLANTS; HAS A FAIR AMOUNT OF JETLINER TFC.) IN ANY CASE; MY EXPECTATIONS BASED ON EXPERIENCE PROBABLY CONTRIBUTED TO MY FLAWED DECISION. BUT I THINK ATC CONTRIBUTED TO THE PROB. FIRST; THE ZSE CTLR SEEMED VERY BUSY; PERHAPS TOO BUSY TO HAVE ACCEPTED A VFR ADVISORIES REQUEST. SHE WAS HANDLING LOTS OF TFC AND SEVERAL OVERLAPPING XMISSIONS DELAYED MY ABILITY TO CONTACT HER OR CLARIFICATION; AND I RECEIVED NO RESPONSE ONCE I WAS ABLE TO MAKE A CALL. SECOND; THE ORIGINAL DISCREPANCY OF INSTRUCTIONS (OK TO CLB IN CLASS B AIRSPACE BUT STAY AT 3000 FT) MAY HAVE SUBCONSCIOUSLY INFLUENCED ME TO DISCOUNT THE ALT RESTR. THIRD; THE ZSE CTLR MAY HAVE UNDERSTOOD (OR BEEN MISINFORMED BY THE APCH CTLR) THAT I WAS IFR; NOT VFR. (MY ORIGINAL REQUEST FOR VFR ADVISORIES WAS CLR; AND THE CTRCTLR ASKED MY INTENDED CRUISE ALT RATHER THAN ASSIGNING ONE; AND DIDN'T COMMENT WHEN I STATED 4500 FT -- SO THAT MAY OR MAY NOT HAVE BEEN AN ISSUE. BUT THE WHIDBEY APCH CTLR WAS UNCERTAIN WHETHER I WAS IFR OR VFR; WHICH SUGGESTS SUCH A MISCOM SOMEWHERE ALONG THE LINE.) ALL OF THIS SUGGESTS TO ME THAT BETTER WORKLOAD MGMNT AT ATC MIGHT HAVE PREVENTED THE OUTCOME. BUT NEVERTHELESS; I UNDERSTAND THAT THIS DOESN'T RELIEVE ME OF MY RESPONSIBILITY TO UNDERSTAND AND COMPLY WITH ATC INSTRUCTIONS.