The reality is that "opinion" is often left out of tweets and direct quotes seem to be the etiquette. I remember a ulearn from a few years back, when we were early to twitter, and the tweets were about the peoples opinion of the keynote speaker, how good bad they are/were. This was embarrassing as the keynote speaker got a bit of negative stuff, we have grown up, but now seem to stick to very safe statements.
Twitter can come back and bite you if you tweet negative stuff, but i think opinion is ok if its clear that its your opinion. So come on guys give us your feelings and opinions. If someone was awesome let us know, send us the link, feed the backs.
Of course there is nothing better than actually being there and networking, thats where the discussion is at its best. Enjoying the conference.