Well, I would like to join the Tara Anti FanClub. I don't like her at all. The only episode where I didn't find her annoying was Once More With Feeling. Apart from that, I could really miss out her from the whole bunch of events happening around Buffy and Co. The only meaning of her being part of Buffyverse (at least for me) was the end of season six, when she died. The reason: her death unleashed the powers lying in Willow, and thanx to this event, season six could have such a great ending with the whole Xander - Willow dialogue in the very end of the last episode in that season.
But the question is: why I hate Tara? Because OK, she annoyed me, but this is just one side of my problem with her. The other is (simply, in one word): Willow. I really loved the pre - Tara Willow, who was just a nice and a bit shy high-school girl. I loved that reliable girl and friend who had such a cool boyfriend as Oz. She was just so different before meeting Tara, and I couldn't get to love the post - Tara Willow as much. Then the Willow - Oz couple was my second favourite couple in the Buffyverse. Then Tara came, and even if Oz had returned, he was shown the door by Willow. (OK, there were tears and hugs while the two of them separated for ever, but still... I missed Oz. I liked him even more than Tara.)