Do all the major search engines treat them just the same as any other domain name? Is there anything about them that a webmaster/seo should be aware of before going out a buying up a parcel of them?
TIA
Yes, no difference.
There has been a lot of comments that the '.biz' domains sound "cheap", suitable only for multi-level marketing.
I don't share that option!
.biz seems to be slow to catch on, but offers a good alternative to other tld's such as .org or .net.
Be very careful in how you buy domains. Whois can be an industrious webmasters weakest link.
>>>>Do all the major search engines treat them just the same as any other domain name
I can't see why they would treat them any different. I see them here and there...mostly affiliates who buy hyphenated keyword domains. I don't really see a lot of "branding" with the .biz's.
As you suggest, if one links their sites together, a competitor can follow the backlinks and check each one for a common owner, but is there some database where one can enter the name/address of a site owner and get a dump of all the sites they have registered?
You can search BIZ listings for owners - which i know of no way of doing with .com, .net, and .org without having to go throw someone who has basically broken someones tos by doing a whois on millions of domains and putting them in a database.
I like us, biz, org, net, and com as they all are under us law and rules (same with some of the other specialty names like .edu, ,.mil ,.gov [and newer ones like .aero](but I don't think I have a good chance of getting one of those)).
.nu, .cc, .md, .tm, .tv is actually a different county (I forget the name), but I don't want to lose my domain, because King Meshoeshoe (a real kings name I believe) decides he doesn't like my site. I don't think there would be much you could do without having to go through that countries legal system.
Just my 2 cents.
Google indexes the names the same. Some other SEs are rumored to place more emphasis on things like .edu and punish things like .cc.