I posted a review on my blog of a new product. Since I was the first to post about it, it became a very popular read, and it was mentioned on other forums, blogs and websites. Its within my target audience(travel), however, its not within the particular niche that my site is based on. My site ranks REALLY high for ALL the major keywords attached to the topic I posted about, which caused traffic to dramatically increase recently. Will google be thrown off by a new keyword becoming very popular for my site, and throw off the actual keywords I am shooting for?
Nope... You are fine... There is no limit to the number of keywords or topics your site can rank for. If you're lucky most of the links will be to the actual post and not just your blog's homepage so that after the post gets archived, it will still have the relevant inbound links... But even if they did link to your home page, it's not going to hurt you or confuse Google at all. My home page ranks for lots of words that appear nowhere in it's HTML.
No that shouldn't be a problem. Google doesn't have a problem with websites that cover more than one niche. Look at how well wikipedia ranks. Really I don't think Google is smart enough to figure out that the new topic does not relate to your niche.
The only bad thing it's doing to you is that your traffic conversion rate has reduced. But you can probably use this for branding as well. Some blogger who is already linking to you (because of this blog post) may easily give you a review or blogroll link.
I never pay attention to overall traffic conversion rates. Typically I only care about SEO and PPC conversion rates and I always track that at the keyword phrase level anyway. I like to know exactly which keyword phrases people search on and the associated conversion for that keyword phrase so I know which words to bid on and which not.