Too much of anything, good or not, in excess can be bad for you. I think crossing that line is different depending on the person. I think it's bad if it's holding you back from doing something that you should be doing and if it becomes the center of your life.
Anime is quite close to the center of my life it would appear. I watch it, I read it, I draw it, I write it, I talk about. I've bought 80+ manga and lots of anime, about 50 GB of my computer is filled with anime, manga, and amvs (some are being held on my dad's computer for storage), the rest of my 180 GB hardrive is mostly filled with my current amv project that's been on there since spring. I cosplay, I go to conventions, I created a local anime club that meets and hangs out once every week or so. I speak bits of japanese, almost anything japnese I encounter gets me excited, I tend to make new friends by finding out they also like anime.
I just love it... to me, it's more than just something to sit by yourself to do. I can create new anime-related things to share with others. I watch anime with my dad, best friend, or my whole anime club (ah it's nice being in charge... kinda). I just have so many great memories from it.. going to conentions with friends. Christmas anime party.... the Anime Masquerade, the Naruto-themed night. Anime helped me get into art again (I've been scraping by without going back to McDonalds from commissions), the fanfiction is what started me writing (I'd like to publish a book), it's what got me to create my first website (I"d like to go into web design and graphic design). I never even THOUGT I could do film editing until I wanted to make an anime music video...
So anime has and does impact my life in a big way--but I think it's been mostly positive. It doesn't cause me to sit in a corner and obsess about it. I let it inspire me to live my life and live it fun. I work when I need to. The anime prince of tennis actually let me found out that I ENJOY a physical activity. I study and am close to my AA degree with a 3.9+ GPA. I try to keep my priorities striaght and put God, family, friends, and school before it (sometimes I might have to work at some of those... *cough* school *cough*).
And it definitely hasn't alienated me from my parents at all. They've made quite an admiring effort to understand and accept my interest. I love nothing more than sitting down with my dad for lunch and asking him what anime we should watch (sometimemes I have to sacrifice and watch the English dubs for him... though he'll watch the japanese if I read the subs aloud
) I've watched a couple whole series with him and he's not to lost if I start going on talking anime... (like going to his room and ranting about the One Piece dub for an hour lol). It's not really my mom's thing so I never pushed that but I think she has a bit of better understanding for it. I got her to watch and like the live-action Gokusen (okay, I have not met anyone who does not like this), and also found a tear-jerker japanese drama that my dad wouldn't be interested in so watch that with her.... so she gets a tast of it anyway. They both have gotten used to me naming new pets japanese names (Kakashi one of our huskies, among our cats are Neko, Kyo, Hatsuharu, etc)--and they might even understand a bit of the japanese I use like Arigato, gomen, hai, (I drill them on it. ^^)
Overall, just keep your priorities straight and you'll be fine. 
I say u cant like anime too much espescailly if u r good at it 
