We've been in the San Juans since March. They're definitely feeling crowded, but it's not terrible, especially midweek. We're anchored in Eastsound now and have lots of room, maybe 7 or 8 other boats here.
The marinas and state parks are busy, especially on nice weekends. Last weekend was packed, probably due to the nice weather and the crab opening.
That said, it's not that difficult to find places that aren't crowded. Just look on a chart, find a bay that's reasonably protected from the prevailing weather but not super close to public shore access, and try anchoring there. Just because a bay isn't written up in the cruising guides, or doesn't have a glowing review, doesn't mean it won't work.
We haven't tried any marinas other than occasional quick stops at Cap Sante, and they've always had space. We stop at SYC outstations every couple weeks and have always found space. Maybe we're lucky.