Google recently announced that they will give a slight ranking boost to websites that secure their connection with a SSL certificate with a key of at least 2048-bit.

Google informed the world that this SSL ranking boost counts only as a 'very lightweight signal' in the overall ranking algorithm. While minimal, the tiniest gain in your ranking can mean the difference between being found or being lost in the masses.

Should I switch to https?

In general, yes. Securing the connection between you and your users will ensure that the data that is being sent between you and the visitor is secure and can not be compromised. Switching an entire site to a secure connection will impact the load on the server and the connection, so it's not all positive. In current times the impact on the total load on the server is not very large however.
The largest concerns come from the reputation your site has built in the past that could be negatively impacted if you switch to https://, which is effectively a different URL.

Google states that they do their best to reduce the impact of switching your website and has given out the following tips to ensure you have the lowest risk when changing your website to use a certificate;

• Decide the right kind of certificate; single domain, multi-domain or wildcard should be used properly
• Use at least 2.048-bit key certificates
• Use relative URLs for content that is on the same domain
• Use protocol relative URLs for all other domains
• Allow google to crawl your website via HTTPS by not blocking it in your robots.txt
• Allow search engines to index your website. Avoid using the 'noindex' meta tag