tumblr has a really amazing community. tumblr's downtime is a fact. The question is, does the community outweigh the downtime?
I think you make this decision based on the demographics of the tumblr community vis-a-vis your users / customers. And tumblr isn't just 14 year old girls -- there's a bunch of tech people on it (although that may be more NYC tech).
In the comments, people have mentioned the simple fact that you can have both a self-hosted company blog and a company tumblr, much like most companies have a company blog and a company twitter. I agree, although simply feeding content from the blog into the tumblr of course doesn't make best use of tumblr as a platform.
My startup's blog is on tumblr (http://blog.idonethis.com) and we get about 1/5 of the referral traffic of twitter and facebook from tumblr. (We have nearly 1k followers on tumblr versus 1.6k twitter followers and 2k facebook likes.) In other words, it's our 3rd largest source of referral traffic from social media.