Changing an email address or phone # is probably enough of a lock-in to be "impossible". Changing the service provider you use otherwise to provide your phone/email/etc., probably a pain, but possible.
Facebook doesn't support indirection (which is why it's crazy that businesses promote fb.com/site urls), but as you've pointed out, it doesn't actually provide a useful service, so if it goes away, no big loss.
It's perhaps somewhat nationalist, but Russian companies are slightly above Chinese companies on my list of "would I want my traffic going through their infrastructure", from a privacy/information security standpoint. I don't think this is irrational. (The US is far from ideal either, but has stronger laws, although is more likely to be "interested". The ideal would be a Canadian or European search provider run in some kind of hostproof model.)
I think over time DDG will do just fine.
What this does is eliminate the biggest point of lock-in to gmail. In the worst case scenario you can switch to another email provider with the flick of a DNS entry, no worries about losing your email address.
Even for search, there are really only a few companies crawling now -- Google, Bing/MS, and Blekko. I'm going to try Bing for a month (I tried in the past, and it wasn't great, but was close) and Blekko for another month, but I'm pretty sure I don't care about any other Google services.