Came here last night with 4 other friends. Was seated immediately. Ordered the following: chap chae, bulgogi, marinated chicken, kalbi, and the seafood pancake. It was more than enough food for the 5 of us. The food was flavorful and portions were sized appropriately. Came out to $21 per person after tax and tip - just a tad pricey.
The food is delicious, and it's open until 8pm, even on Sunday... if you live in SoMA/South Beach, where the streets roll up at 6 (and the restaurants at 4) you'll understand why that alone is cool. I liked the vibe of the place, and there's a great plaza out front for sitting.
Cha Cha Cha's is a great place to go on the weekends. It can get pretty crazy busy, but for the most part you can sit at the bar if you can spot a group about to leave. The sangria rocks, the tapas are pretty good, but at times the service is lacking.