The rivalry between Boston and San Francisco is heating up — at least in the realm of startups and innovation. In biotech, experts say, Boston has a higher density of companies, research groups, and anchors like Vertex, Biogen Idec, and now Sanofi; meanwhile, the Bay Area has more diversity, a bigger feel, and maybe, bigger dreams.

But there’s a new wrinkle: California is about to hit small-business founders and investors with a big retroactive tax.So, look into that before you move your startup to Silicon Valley.

In other innovation news…

EMC and Lenovo have started a joint venture with a new office in Hopkinton. The goal is to help Lenovo get into networked data storage while improving EMC’s sales in China and other emerging markets.

Our startup of the week is Boston-based Apperian, a mobile software firm that’s just raised $4 million from Intel Capital, bringing its total venture backing to $28 million. Apperian is trying to be a one-stop shop for companies to deploy and manage mobile apps.

And lastly, one of Boston’s more recently public companies is on the move. Carbonite, which had its IPO in 2011,is moving beyond online backup and into file sharing and syncing. That puts the seven-year-old firm in the company of Dropbox and Google, which is probably a good thing. Though I’d say California does have the edge there.