Meyer lemon tree needed harvesting: 3-4 dozen, then put in veggie drawer + forgot. How to use now?

For making marmalade with Meyer lemons, yes all-Meyer recipes are good.
But/and I've had good results and interesting flavors using a variety of citrus in a recipe for 3-fruit marmalade. That's usually lemon, orange & grapefruit. But use whatever is in your market or CSA box...citron, Buddha's hand, etc.

I am apparently very susceptible to suggestion. I just impulsively picked up a 4 lb box of big, juicy Meyer lemons at Costco. About to embark on my maiden canning attempt, making marmalade. If you hear about anyone dying from a marmalade related incident, we never had this conversation.

I agree with several respondents, juice, zest, taste, then proceed. If the juice is at all spoiled, toss it. If not, freeze it. I occasionally will find a cut and saved lemon to become a bit bitter, but this can be used to advantage in some applications- salad dressings, etc. If your juice is not spoiled (no mold or slime on fruit), then use your judgment on where the taste is best used. I will add, zesting soft lemons is a pain in the...
I might also add, is it possible that you are doing what I often do? In an effort to use up something nice, but past its prime, or not really my favorite (a bushel of organic okra, say) I will rack my mind, spend more money and time than the item may be worth, and have in the end a boatload of something just okay, in this case not-quite-great lemon juice, or a pile of okra pickles (I hate okra). I hate food waste, and will always look for a use, but the way to make lemonade from this situation might be to toss the fruit.

Meyer lemon marmalade - I made this recipe (http://www.simplyrecipes.com/recipes/meyer_lemon_marmalade/) this spring, it turned out great. I used it for lemon tarts for a bridal shower, but had a little left over and found it worked great in quite a few savory applications as well.

For lemons in general, stilltasty.com says they keep one week in the pantry, 2-3 weeks in the refrigerator, and 3-4 months in the freezer. My experience with home grown is completely different. At my house, they take months and months to ripen on the tree, I let them sit for weeks on the counter, and then I move them into the refrigerator for some more months and months. I never get to the freezer, as I'd end up with a freezer-full of old lemons. I haven't used Meyers or Eurekas for limoncello, as there are better varieties. The Meyers don't keep as well as the Eurekas, and it sounds like yours are way past their prime, and yours don't sound like the best of candidates for much of anything. Have you tasted them? When a lemon gets beyond soft, headed to mushy, it may be time to compost.

I might not be too late to make preserved lemon with them, since those get soft and mushy in the preserving process anyway.

Possibly "You'll remember next time" is the answer- if they've gotten to the point of off flavor, maybe it's time to let go. Meyers are astoundingly productive, even tiny trees, and can be pretty hard to keep up with.

Thank you, all Answerers; but note, these lemons are now soft, headed to mushy. I need solutions that will accommodate the changed flavor profile of these neglected citrus fruits... (I think?) (Maybe booze - Limoncello - IS the answer? >;-)

And here is the recipe (Amada's!) I've used for years to make a delicious Meyer lemon tart: http://cooking.nytimes.com/recipes/1013-meyer-lemon-tart

Here are some ideas, 100 of them in fact: http://www.latimes.com/style/la-fo-meyerlemons16jan16-story.html

I just read the 3-4 dozen part. Maybe freeze in larger containers. Lemon curd and preserved lemons are a good way to use up lots of lemons. Lemon meringue pie too.

Yep..dehydration. The fridge is not a great place for citrus. The good news is that they didn't mold. I'd zest them, juice them and freeze both in ice cube trays. Or..send them ASAP to me since Portland seems to be having a hard time finding Meyer lemons.

If you juice them to freeze, make lemon curd or whatever, you can first use the peels to make homemade Limoncello. Very easy, and especially delicious with Meyer lemons. http://www.thekitchn.com/how-to-make-limoncello-cooking-lessons-from-the-kitchn-197694

Juice & freeze would be the simplest way to handle these.