What are peoples thoughts on domain extensions such as .dentist or .media? Would you ever buy one for your own business?
Yeah, there's no reason for a new extension not to to rank as well, and if it means you can have a domain with more relevant keywords or a better name, then it'd arguably be the better way to go.
A web designer or creative agency could get away with a newer extension I think, at least if you're not targeting small business owners like plumbers and so forth.
My understanding is that .biz and other spammy/weaker looking domains as you put it are seen that way by users, but not by the search engines. And it should have no impact on ranking.
4. Non-.com Top-Level Domains (TLDs)
When a webmaster registers a domain name, they will be given the option to buy additional TLDs. In order to maximize the direct traffic to a domain, it is advised that webmasters should only buy a domain if the .com version is available. Additionally, it is not recommend that SEO-conscious webmasters purchase low quality TLDs such as .biz, .info, .ws, .name, etc. as a means of increasing traffic.
According to Matt Cutts—the renowned webmaster evangelist working at Google—gTLDs such as .gov, .info and .edu do not receive a special bonus or penalty regarding their ranking compared to "common" gTLDs such as .com or .org. But he added that their are thinking about the fact that some gTLDs—e.g., .cc, .ws, and to some extent .info and .biz—are getting abused and may be treated differently in the (next?) future.