I have noticed that when I have a full battery, my Sprint Pre Minus works acceptably with 2.1.
However, once it reaches the low 20% range or lower it can barely unlock (lagging by as much as 10 seconds) and I can get "Too Many Cards" with no cards launching or running at all.
This has lead me to believe that 2.1 has some kind of throttling of CPU that underclocks as the battery gets depleted.
If this observation or info is in another thread, please point me to it. The info is so fragmented it's not easy to track down such info.