There comes a point in any technology discussion where you reach your limit--the point where you frankly don't care about the topic any more. The topic may have gone over your head, or it may just plain bore you silly. Yet your Nerd continues to go on, drowning you with minutiae. This is where my favourite technique comes in to play: the Nod and Smile.
Here's how the Nod and Smile works. You make eye contact with your Nerd and you give them a little nod. What you're saying is, "sure, yep, uh-huh"--basically, that you get what they're talking about. Then you smile. The smile reassures them that you're on board with the discussion. Yeah, who am I kidding? If you do the Nod and Smile right and your Nerd is paying attention, they'll realize that you've lost interest in the conversation and reign themselves in. It won't happen right away, but over time they'll realize that this look means that you have effectively "checked out" of the conversation and they are in fact talking to themselves. Sometimes they just need to get the technobabble out of their system. If you need a break, suggest they contact one of their Nerdy friends. Just be aware that when Nerds congregate, the talk continues to get louder and more technical as it goes on. You could lose your Nerd for some time or be pulled along into the technobabble with them.
The Penguins of Madagascar have a version of this called the Smile and Wave: