I don't have a Nexus yet, but I'm considering moving to it from the EVO. At first, the lack of external memory card was the main reason I didn't want to get the phone. But the more I thought about it, the more I like the idea of storing to the cloud, so long as I can download easily to the device when I want to listen to something so I don't have to stream.
The main reason I like the cloud idea is the fact that I've been through three micro SD cards on my EVO already. Seems after a certain number of read/write cycles, they corrupt. Since you have to buy them online to get them cheap, you have to wait for days to replace a corrupt card. PITA. With a Nexus, I'll never have more than 16GB on board, but then again, I won't ever have to replace another card, either. I'm playing with Amazon's cloud service now. It seems to be working well enough that the external storage is less an issue than it was.