when I add a Tumblelog, it only adds my first blog. I can't add another blog for some reason.
Add another stream (Add Stream > Apps > Tumblr: My Tumblelogs), then when the stream has been added, click the name of your blog at the top of it, and select whichever one you want that stream to display. It seems to work for me with two blogs (both on the same account), even if I leave that tab and return to it -- I have one stream for each of them.
Hey Max, in your "My Tumblelogs" stream are you able to click the settings "gear" icon and see all your different Tumblelogs listed? Also, if they are private -- they won't be listed for use at this time.
You should have access to all your non-private Tumblelogs from the settings drop down. We're working on a fix that will keep the stream logged into the selected Tumblelog without reverting back to the first one after leaving the tab.