I designed my kitchen with a long uninterrupted plane of space for cooking projects, my island is just shy of 7ft long.
It was in heavy use this weekend as I was filling my pantry and my freezer to process garden bounty. Canning benefits not only from the island, but also the 60" behind the island and adjacent to the stove. 14 pints of dilly beans, 8 pints of bread and butter pickles, double batch of granola, washing and tying up 20 bundles of oregano for drying, 4 qt bags of shredded and drained zucchini, 4 qts of green beans, 5 of broccoli, 1 gallon of refrigerator pickles, 2 loaves of zucchini bread, and a blueberry dump cake.
I regularly make bagels, muffins, and bread.
The space is awesome.

70" on my island. My DD who bakes uses the island mostly.

I have a 9x11 ft small kitchen with a 7 ft long, uninterrupted countertop that's 26" deep. I use it that space for all dinner preparation. The deeper top also makes it easy to make bread, sourdough, biscuits, etc. There's enough space to roll out dough with a couple of items (like fruit) setting close to the wall. Love it!!

There's a 7.5' stretch on my island, plus a prep sink. I most intensively use only about 4' of that for baking. The best part is using a bench scraper and cleaning the counter off right into the prep sink. Cleaning up after bread baking is no longer a chore! I know you didn't ask, but I thought I'd mention that part. ;)

I have one section that is a little over 12' long (peninsula), and it is great for laying out cookies to cool, or for informal buffets. I also host the neighborhood ladies for Christmas baking, or the neighborhood little girls for baking, and this long counter works wonderfully. The island is also 7' long, and I do my "rolling out" there...pies, cookies, etc. I honestly don't bake that often for just the two of us.

16' 10".
I barely cook, but I like the look.
Made it my own bad self.

A 7 foot long island. I will use it for bread baking, pastries, chocolate, cakes and cake decorating, candy making, basically any kind of pastry/baking related thing you can imagine!

fouramblues: ok, now I want a prep sink in my island. I never thought about how convenient it would be for cleanup.

Right now? About 4'. But, there's a ton of stuff on the counter that has no other place to live, so effective space is really more about 3'. In the new kitchen, we are putting in an island (narrow because our room is narrow) and it will be 6' long. I wish that we could put a prep sink in it, but it just won't work out for us. Even without a prep sink, I'm thrilled to get a nice long work area.

I have a 10 ft island with a prep sink at the end plus 8.5' of uninterrupted counter on the main kitchen wall. It is great to have so much space.