I love absolutely every single thing about rimming my girlfriend. I love it just as much as eating her pussy, but it feels even more intimate and special. I have always found her anus to be perfectly, scrumptiously beautiful, and I can't imagine not wanting to explore and savor her erotic needs there. And yes, the taste is exquisite. I especially like it if I can coax her into letting me tongue her little hole just after she's been out walking or working out. I love her natural taste. If anything, she's too worried about being clean (she always makes me wait until she's done a quick "spot cleaning" before I can go down on her and it always saddens me that she's washed away her own juices). For me, her asshole tastes pretty much just like her pussy, but "brighter". It's hard to describe. The first time I was able to push my tongue fully into her anus, it was like licking a battery--everything tingled and my tongue felt sparkly (although that was probably more a psychological response on my part).
It took a looooong time to get her to let me tongue her asshole, but it was worth it. It started with making extra licks a little too low when I was going down on her that got a good response, but she said that although it felt good, she didn't think I should be doing that. Once, she let me drizzle honey all over her butt and lick it off. I made sure a lot of it fell right on her anus so I had to spend a lot of time there, being very thorough in order to get it clean.
These days, I can usually get away with bending her over the bathroom sink when she's getting ready for work or bed, pulling down her pants and panties, spreading her cheeks, and thoroughly tonguefucking her pretty puckered hole. And whenever she's giving me a handjob, she'll climb over my face, 69 style, and let me lick her butthole to my heart's content. I love it, because I can push my tongue into her really deep from this position, and she really starts to moan.
The only thing I wish would change is that she rarely lets me finger her clit and get her off while I have my tongue up her ass. I don't know why, since it always makes her really wet, and the few times we have finished her off that way, she came like crazy.