I think personally the best thing about beer can chicken is, that you can fit more birds in your smoker/grill.
I love BBQ chicken and make it regularly. Here's two birds I made last weekend in my Weber kettle.
This one the previous weekend, without the beer can, just lying down in the Weber kettle.
Do I taste any difference with or without the beer? No I don't. Either way nice, juicy and succulent chicken. Nice rub, basting with Stubb's BBQ mopping sauce (haven't found better baste yet) and smoking them with cherry or apple tree for about 2 hours makes the chicken just about perfect to my taste. First hour low and slow and raise the heat to about 300F for the second hour to crisp the skin = heavenly chicken!
To be honest I don't like moist chicken, I like it on the dry side. So I've never done the beer butt, but I do marinate in beer and spcies, and highly recommend it.
I have done the beer can whole chicken a few times but i have to agree here it becomes almost too moist - i like it more on the dry side i guess. Thats not to say i don't like the whole idea of the beer can chicken and it does taste great!