I recently bought a Yeti tumbler...for $40! I was on the fence buying one but a friend had one at the beach drinking a frozen slushy vodka drink out of it (Pinterest search "frozen vodka drinks" and there are a ton out there). What impressed me was the entire time on the beach her drink stayed slushy in the cup (impressive).
I bought one at a local store and waffled between the 20 oz and the 30 oz. Another friend who has one said 20 oz but I thought "go big"....I wish I had "gone small". The 30 oz is excessive and not easy to handle but oh well...lesson learned...when I add my vodka slushy drink I never fill it up to the top...I usually stop half way (so a 20 oz would have worked).
This is a first generation product and it needs some improving. It definitely keeps ice and drinks colder then the Tervis tumblers I use. Recently I parked my car for 3 hours and left my Yeti tumbler in there (with ice and water) and everything stayed COLD (some ice had melted but I still had ice in it). I took my Tervis water bottle filled to the rim with ice and water and walked a beach for 2 hours with it in a drawstring bag and the ice was melted and the water was lukewarm. It outscored the Tervis in that regard hands down. Where it fails is its lid, ability to carry easily, and coloring.
If you look at the second picture you will see that the Yeti lid has a drink opening but no way to secure that opening. My Tervis cups all have a way to lock down the opening so if I accidentally drop it or knock it over water isn't going to come gushing out. Not so with the Yeti. I have knocked mine over, had it tip over in a beach bag, and fall forward in my moving car and had to mop up the mess afterward. They really need to design a better lid (really how hard could that be?!?!). Another problem with the lid opening is that it is small'ish. You can't put a hard straw through it. You can put a straw in it that you can bend flat to slide in but since I have a lot of hard straws that doesn't help me.
The second problem is the ability to carry it easily. Part of that has to do with sloshing water out of it because there is no closing...so you have to hand carry (you can't throw it in a drawstring bag if you go walking or biking - so using it for exercise is out for me). The other part is that it is noticeably heavier than a Tervis and a bit more awkward as far as handling. It is almost impossible to hold the Yeti and any other object that might be in your hand. I like my Tervis water bottle design (see last picture) where I can loop a finger through the ring to carry (instead of using my whole hand).
My last complaint is the coloring. There is only one color...metallic silver. That makes it hard to identify when you are with other Yeti users. I went to a craft fair and had a name plate put on mine by a vendor ($5 - see last picture). If you Google "Yeti" on Etsy there are lots of places that sell monogrammed stickers and etching options for Yeti identification (some at a reasonable price). Since you have to hand wash the cup (no dishwasher like a Tervis) any vinyl stickers should stay on quite awhile. Tervis offers a ton of coloring options and I would think that Yeti could offer some generic ones as well (see my generic South Carolina Tervis above).
Bottom line - I will use my Yeti in situations where I am not moving around a lot (i.e. staying at a desk all day or trapped in a meeting). I'll fill it up at home with ice but fill it with water on site as opposed to at home to avoid spillage while moving between home and work (I teach and carry a bunch of bags and supplies between schools so it is 100% guaranteed to spill if I tuck it in any of my bags filled with water).
I'm hoping they improve upon these design flaws so I can use it more of an "every day" tumbler as opposed to an "occasional" tumbler.