Dell Streak won’t turn on without back cover
If you use several microSD cards with the Dell Streak and also unlock the UK version so that you can swap SIMs, you may be interested in knowing that the device won't turn or stay on when the back cover is removed. So even though the microSD card is accessible without removing the battery, don't expect to be able to flip the Streak over while you're using it, pop off the back cover, put in a new card, and just continue doing what you were doing.
The back cover is easy enough to take off and put back on, but if I know I won't be using the Streak for very long (e.g., transferring content from a microSD card), it would obviously be faster to be able to leave the cover off. The only reason I discovered the cover/safety/lock switch in the first place is that I was testing SIMs and wanted to know if they would be recognized. Since it would only take a moment to find out, it didn't make sense to keeping removing and replacing the back plate.