I'd expect in a tabbed browser, any new window links would open a new tab if you've got the browser set to *gasp* open windows in a new tab. Blame the browser if they open in a new window when they've designed the browser to use tabs.
I expect links to another site to open in a new window. It just makes sense, I'm leaving the site, you don't want me to completely stop seeing your stuff, so keep your own site open. I don't see how it's so terrible to have a new window open. That's why we have an OS that can have different things in different windows. Otherwise we'd all be using AOL's interface (or actually one even less useful, it'd be DOS-mode).
Especially in a forum environment, if I'm in the middle of a thread, I'd like to just be able to click a link which is being used for descriptive purposes and have it open in a new window, so I don't lose the thread. On some sites you could just hit the back button, but Fusetalk seems to have difficulty working properly with IE (whether IE properly works is irrelevant), so you end up with pages expiring and having to be refreshed and submit data again, or you lose entries in a text form or something like that. Pop up a new window, read the content, close the window. Simple, easy, exactly what a windowing OS is intended to do.
But personal preferences aside, I just want it to always work the same way at least on a particular site. This WYSIWYG editor seems to have a lot of glitches like this.