On the whole, I find that placement impacts usability far more than appearance.
Consider the behavior of this comments form: because the "Post It!" button immediately follows the last field, its purpose is obvious regardless of its appearance (excluding the label, of course... if it said "Purchase This Kitten", for example, I'd likely be quite confused).
Compare that to the positioning of the Notes client action bar; although I found and experimented with code allowing Domino apps to lock the action bar in place, that ironically confused some of my long-time Notes users... in Notes they're used to the bar staying put, on the web they're used to having to scroll.
Button or link, if the placement makes sense, the user will - more often than not - know intuitively what to do.
On the whole, I find that placement impacts usability far more than appearance.
Consider the behavior of this comments form: because the "Post It!" button immediately follows the last field, its purpose is obvious regardless of its appearance (excluding the label, of course... if it said "Purchase This Kitten", for example, I'd likely be quite confused).
Compare that to the positioning of the Notes client action bar; although I found and experimented with code allowing Domino apps to lock the action bar in place, that ironically confused some of my long-time Notes users... in Notes they're used to the bar staying put, on the web they're used to having to scroll.
Button or link, if the placement makes sense, the user will - more often than not - know intuitively what to do.