What does support mean?

I'm trying to throw myself into supporting the eBook community. I have an eReader now, I'm plugging into the blogs and news, etc. But now I'm up against an important question:

Can I do honest reviews of eBooks as an author?

I want to read some of the new entries in our community and give my opinion, but quite frankly the first couple of books I've tried were - well, crap. As in, if I want to stick to the 'if you can't say something good, don't say anything at all' maxim, I should just keep my mouth shut. However, that is not being honest as a reviewer. If I really want to offer reviews, I need to be truthful about the good and the bad.

However, if a lot of my reviews bash other authors it just looks like I'm being petty. Maybe I should hold off on the whole reviewing idea altogether? Can an author be a reviewer and still be taken at his word?