Back when I had the Nexus One on Eclair (2.1) I ran into the "Low on space" issue and it was slightly aggrivating.
This is completely inexcusable however. I shouldn't be plagued by such an aggressive bug, and cross versions, cross devices. Google really needs to start working on usability issues and spend less time on new features. Remember the SMS bug that lasted for years? I am a huge fan of Android. I've been a fan since they announced it, made mockups a couple of years ago of Android on a PSP2, spent the past year learning Android in college. Right now I'm trying to find a job as an Android developer. I love the OS, but this is ridiculous, and as a fan I feel I have the right to say, WTF Google?!
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Also, make sure to actually shut down the phone once every few days. I got that advice quite a few years back when I was in high school and I find that it is still applicable today. Smartphones tend to like getting that fresh start.