It needs to work, and aside from that, it should not be obtrusive. It might not be of importance to the fish, but a nasty one might be.
I've come a long way with heads in the past couple of years. I just didn't know any better, and that reflects my skills throughout the construction of the fly. In other words, the eye is a visible reflection of the care and ability applied to the remainder of the fly construction, seen or unseen. I know my tying improved by leaps when I started being very particular about where I started the tie-in, and how many wraps for this or that, and flattening the thread...etc. Watching you guys describe your methods over the past couple of years has been the greatest influence on my tying and certainly expanded my enjoyment. The eye just reflects the attention to detail in the entire fly, and especially on a spider where there just isn't a lot to critique.
look at this from IBF Swap #1 in 2006. It's neat, but to me it's embarrassingly large.
This is what I aim for. Sometimes I get it, sometimes not. 2008.
I haven't used cement in a couple of years either, since I went from a piled up, double 4-wrap whip finish, to a clean 4 turn whip finish. I have never had a fly come undone...on the front end.
w
, I'll agree my tying is better, but you're much too kind. Wait until you see my hair-hackle fly from the IBF Swap 11, you'll have to take it back. 
