I believe you are referring to the table of your collected responses in "View Responses" tab, is this right? if so, you can select "Filter" on the toolbar, and define your criteria in the filter dialog. Depending on how you would like your conditions to match you will select either ALL or ANY at this "Show only rows that matche ANY/ALL of the following:". To hide a column in the responses table, you will have to do it manually, by selecting the column and clicking on the drop down arrow next to the letter on top of the column and select "Hide Column". Please try out filtering and hiding column or either one and see which one works best for you.
If you are referring to the form filler seeing or not seeing certain fields based on the responses collected, then, we do not support this feature currently.
Hope this helps,
OK - I found the filter for category that "isn't blank". It would be nice if there was a way to select "isn't blank" for all categories, as it's quite tedious to add that filter for all 50 of my fields...
It would be also nice if you could save certain filters. (ie. I could save a filter that shows 7 certain categories, and another that shows a different set of categories).