At least one person at the NEVA2013 meetup didn't recognize the piece of rubber on my left thumb, and I haven't found a mention of it on this board yet, so…
I like to ride with a light elkskin leather glove in the summer. I'll also choose an insulated leather deerskin glove in cool weather that doesn't require heated gear. Unfortunately, neither of those pairs includes a squeegee on the thumb like my heavier gloves.
Enter Aerostich's VeeWipe. It's a squeegee attached to a thumb-size rubber tube that can be worn over any glove.
Aerostich VeeWipe Squeegee :: Aerostich/RiderWearHouse Motorcycle Jackets, Suits, Clothing, & Gear
I've had mine for two or three years now. The package comes with three sizes. I use the smallest with my thin summer gloves, and either the smallest or the medium with insulated gloves. They stay on well if you choose the right fit, and really tug them down when first putting them on. Unfortunately, I've now lost the medium and large size ones due to using them with the wrong gloves. I'm hopeful that they'll eventually sell a multi-pack of just one size, instead of only the assortment.
They work great, though, as long as you've taken care to place them where you want them initially. Easily as good as any other glove squeegee. I just keep the small one in one of the pockets of the gear I wear every day, so I always have it if I find unexpected rain.