....25% of the visitors who land on the homepage go straight to the search ....Opinions, personal habits, speculation and authoritative replies all appreciated.
This one is speculative.
Hard to say. One might assume that 75% are navigating, but you don't say what percentage come to the home page and immediately leave (use neither search nor navigation). Let's say for the moment, your homepage bounce rate is in the single digits. That would mean that nearly 3 out of every 4 people choose to navigate.
Is that good or should it cause concern that the linkage pathways are not meeting the needs?
I had the opposite reaction. To me 3 out of every 4 people navigating would lead me to the conclusion your navigational structure is good. I think it were confusing or not obvious, most would choose to search rather than navigate.
I think the size of the site or perception of the size of the site has a lot to do with whether people choose to navigate or search. With 150,000 product pages, my site tends to be a monster to navigate trying to fit them into about 1,500 categories (which includes sub categories and sub-sub-categories) and would guess my stats are the opposite of yours (that more people search, rather than navigate).
With a smaller site with less pathways, it might be easier to navigate.
To me, the more important question than the split between navigation and search is "did they find what they were looking for?"
Again, the above is speculation.