Kari Whalgren voices absolutely loads of characters in all kinds of games and anime. She was Shelke in Dirge of Cerberus, too, and so many times I've watched a random anime series and recognised her voice playing some woman. The PW fandom is in almost universal agreement that if there's a PW anime, she should voice Mia. And Cam Clarke should be Edgey :)
Tara being evil was a huge fan theory for quite a while; it doesn't surprise me, especially since it took ages to get an explanation for her deliberately messing up the demon locator spell in Goodbye Iowa, and the logical explanation was either a) she was a demon, or b) she was working for the bad guys and didn't want the demon found (though that makes less sense, since they were looking for a polgara demon at the time and it wasn't a polgara but actually Adam, who probably wouldn't have shown up). But yeah.
I've seen Willow/Jenny fics before. One-sided ones, but still. I think it's fairly adorable (less weird than Willow having a crush on Giles, which still disturbs me), and it would've been awesome if it'd been mentioned in canon.
I admit your "It just annoys me so much that Willow shows no interest in boys and then suddenly becomes exclusively lesbian." made me giggle, but I know what you meant. It was fairly annoying that her sexuality did a complete, unexplained (Amber being gorgeous notwithstanding) 180, but it wasn't entirely sudden; as early as A New Man (the first time W&T met up after Hush and did the rose levitation spell), Willow lied about where she was to Buffy, so one assumes she realized there were feeling fairly early, but they aren't really addressed at all until Who Are You?, and not explained until New Moon Rising. Plus, as I think Butterfree mentioned before, in late S4/early S5 there are a couple of instances where Willow does mention attraction to guys (Giles in WTWTA, Dracula in Buffy Vs. Dracula), but by mid-S5 these pretty much stop happening and she identifies as a lesbian. It was a 'figuring out' thing, as explained by canon (and quite adorably by Willow in Hell's Bells; "It's a good thing I figured out I was gay, else... you, me... formal clothes..."), but not explained very well at all at the time.