It's not the SD Card. Since I purchased a new one, I've had absolutely no issues with it unmounting and I've had the new SD card in it for a month. I've done absolutely nothing different...actually use it LESS now that the initial *oooh new toy* has worn off and all of these issues I am having are new within the last 2 weeks.
The only thing that has been ongoing is the crappy battery life. I am constantly in a low signal area...my home. I only have 2 bars at home. I found that my wi-fi uses less than the 3g, so I keep the wi-fi on at home. I don't really use any of my apps and they are all turned off sync.
Here's my apps:
Adobe Reader
Gmail
Yahoo Mail
Kindle
Angry Birds
Astrid Tasks
Chase
Facebook
Flash Notify Settings
Google Sky
Nook
Open Sudoku
Pandora
Quick Settings
Retro Camera
TV Guide
Wordpress
None of which I really use...If I'm out of the house I might use Facebook one or twice, Angry Birds 10-20m a day...but other than that it's just a few text messages and emails.
I got better battery use when I was abusing the phone listening to music and playing angry birds all day than I do with it sitting on my desk. I barely used my phone today...2 texts, 5 minutes of email app and 5 minutes of angry birds the rest of the time it was in my bag. It's been off the charger for 7 hours and i'm at 50%.