When is it the end of beacon season?

For me, the question goes in reverse: When is it beacon season? I have one and do carry it, but very rarely and I often forego it even in winter. Had a great trip in the Canadian Rockies the week before last and it's easy to visualize summer avalanches happening up there, but I didn't regret leaving my avy gear in Vancouver for one second.

An ounce of prevention is worth a pound of cure. $0.02.

I'm such a waffle. I always go with the group consensus. I bring it to the parking lot, then decide with everyone else.

I'm with Ron. If the snowpack is totally isothermic and I feel really secure, but my partner wants to wear 'em, I'm down. It's not that much weight to carry anyhow. I'd rather have a good time out and have everyone feeling good about it. It's always with me - either on me or in my car.

I'm probably more casual about beacon use in spring than most people. (I'm not saying this is a good thing...)

When I think the risk is mainly point releases, not slab releases, and when I think that the main hazard is being swept over cliffs or other terrain traps, rather than burial, then I tend to leave the beacon behind. This usually takes place sometime in the latter part of the "mush season."

But if the rest of the party wants to carry beacons, I'll definitely carry mine.

Of course, each situation is different, but by and large, one needs to look at the nature of the risk at any point in time. As Lowell mentioned, when the risk is from sluffs and not slabs and primarily from injury instead of burial a transceiver is not of as much value. I don't think there is much literature in this regard but it is far more difficult to get buried in heavy wet snow as it is in lower density dry snow just because of volume and density considerations. But that doesn't mean that wet snow avalanches aren't dangerous, it just means the ways that they can get you are likely to be different. I have a huge amount of respect for any wet snow avalanche risk because of the risk of entrainment and/or injury due to their greater mass per volume.

It's not necessarily a seasonal thing for me, just route and condition dependent.  Unless weight is a really critical factor for pulling off a trip and/or avie hazard is quite low, I typically just bring beacon and shovel as a matter of routine.
My thinking is along the lines of "how stupid am I going to feel if I don't have my beacon the one time I need it?"  and "what is the benefit of leaving this stuff behind?", I try not to fall into the trap of caring what the locals and experts are doing or recommend unless I am as confident as they are in assessing the hazard.
The goal is always prevention, but I've never seen much reason to spend a great deal of time or energy rationalizing leaving beacon and shovel behind.  It's just not usually that big a deal to carry the stuff. 
I did go on a trip Mon/Tues and left the shovel behind, beacons were turned off in the pack then left behind in the tent.  We were confident the hazard was manageable and felt the weight would hurt us.  Like most people are saying, we agree on a decision based on the trip and the anticipated conditions.