My own impression of Yahoo from years back is that if something as critical as the YUI toolkit sucked, which it did, then Yahoo had limited prospects.

Perhaps an odd thing to base an opinion on, but compare stock charts on Google versus stock charts on Yahoo. The Yahoo ones were clunky and sucked.

Compare Yahoo Mail with GMail, and Yahoo sucked in comparison, being riddled with giant ad-banners.

Even now, Yahoo search results suck, which is really noticeable when FireFox periodically resets my search engine to Yahoo. Suddenly my results suck, and back to Google I go.

I don't know what Marissa Meyer has been doing, because it doesn't seem to be apparent in Yahoo getting better at anything really.