I cook a lot of Thai food, and Viet Wah is by far my favourite place to shop for ingredients. Their veggies are always good and fresh, their seafood (while it may look less enticingly presented) is excellent, and their dried good selection has some hard-to-find stuff. Most of the time their prices are very cheap vs. Uwajimaya.
I used to enjoy shopping at the old Uwajimaya downtown. The ambiance was always great, and I felt like I was in another country sometimes. The new one has good selection, but it feels too "Whole Foods" and less authentic somehow. Viet Wah brought back what I used to love about the old Uwajimaya.
To give you an example of prices... I bought Rainier Cherries at both Whole Foods and Viet Wah in the last 2 weeks. At Whole Foods, I paid (foolish me), $9.99 a pound. At Viet Wah, I paid $1.29 a pound!!
I've also stopped buying seafood at Whole Foods and shop at Viet Wha for it - the quality of things like shrimp and fish is FAR superior. I've had very inconsistent experiences from WF.
Oh - added bonus. The Tamarind Tree restaurant is in the same parking lot, if you're feeling peckish :)