Monsters and Manuals did a very good blog post a couple months ago on dynamic encounter tables - something similar to what I had been doing for some time, only I use the encounter tables in the 1st Edition Dungeon Master's Guide modified by the Action and Subject tables from
Mythic Game Master Emulator.
The one big problem I have with the way TSR/WotC (and Paizo & others) have handled random encounter tables in the past is that their tables don't supply the DM with action or context. Instead, they rely on the DM to come up with interesting context in the moment. In my experience, this often leads to the DM defaulting to running the same basic encounter only switching up the type and quantity of monster. This often leads to boredom at the table.
An encounter table that says: 18-23 - Goblins (2d6; 20% chance in lair) doesn't really tell me anything. Who are these goblins? Why are they there? What are they doing? Dynamic encounter tables (such as the ones suggested at Monsters and Manuals) help answer these questions.
I'd hope that WotC follows Mythic in showing potential 5th Edition DMs all that can be accomplished by using random tables to push adventure.