not with droid x's large internal memory. there is a disadvantage, some claim apps moved to sd card cause the dx to reboot when you plug it into your computer while in usb mass storage mode.

 

When you plug your phone into your computer in 'Mass Storage' mode, it does indeed unmount the SD card and you can't use/view anything on it. Some people also say that apps run slower if moved to SD, but I haven't noticed it, and it wouldn't be MUCH slower.

I've moved a few in the past, but like Mruno said, there's sooo much internal memory on this phone, it's not necessary at all really.