I can deal with having to export my files in case of acquisition, but it will keep me from suggesting this service (which sounds awesome, by the way) to non-technical friends and family.
That aside, I do see your point, but to say that you will not recommend a really nice service to your friends and family on the sole basis that they are a YC company seems odd.
It sounds like you're describing a problem all startups face.
My concern is recommending the service to my 70 year old father and getting a confused phone call from him about why his bookmarks are broken and instead lead to an acquisition notice and then having to walk him through the export process.
In other words, the value to me in recommending these services to my friends and family is 1) that they'll use them and see some benefit and 2) that I won't have to support it.
And, at the risk of getting all patio11, you know who spends a lot of time organizing photos? Older folks and housewives; NOT Silicon Valley wunderkinds who are trying out the latest and greatest YC company which got a mention on TechCrunch. The problem this team will face is that you have technically literate people like me standing between them and the non-technical friends and family who will shell out $20/mo until the end of time to organize and share photos of their grandkids.
If this is just a tech demo before a FB acquisition, disregard the whole thing though. :)