You wouldn't have to trust them if they made the client open source. It still baffles me that they're aren't doing that given that their entire sales pitch is about security and privacy and "no knowledge".

I'm a paying customer and I use SpiderOak for some non-critical backup/synchronization tasks but I refrain from using it for anything sensitive because of this.

I'd also like to be able to hack the client to remove all the cruft I don't need, it's not exactly pleasant to use currently. On linux I'd actually prefer a good CLI over the weird GUI we have now.