I know and I researched quite a bit before making the jump.

Basically there are couple of things which make me think they won't just shut down:

• They've been around for quite a while (10 years as of now)
• They're betting on the ever decreasing costs of storage to manage their margin
• They still try to sell you complementary products
• They don't ever have to increase your max storage unless you pay again
• They still have monthly subscription available

All in all, I've felt pretty safe using them and I've done the cloud provider switch once so I can do it again