Zymurgy Mag published an article in the July/August issue, Liquid vs. Dried Yeast. They did a comparison of White labs WLP051, Wyeast 1056, and Fermentis US56 dry ale yeast. They also pitched one carboy with half half dry ale US56, and dry Lager W-34/70 also from S.I. Lesaffre. The White lab sample took off first, 12 hours, and the Wyeast took the longest to get going, 24 hours. After conditioning, there were only slight differences in nose, taste, and finish. Oddly enough, the two liquid yeasts were the two with the most differences. They said they enjoyed the ale/lager dry yeast batch best overall.
I like the convenience and lower price of the dry yeasts, and more quality, varieties are becoming available including Belgian yeast strains.