1. I've found it would be nice to have on the search page radio buttons for All and Original posting so you can filter search results and view just original postings not replies
I for myself think, that this would not be very useful. I search for keywords and in the moment of search I don't know, wich entries will match the keywords. I wouldn't want such a constriction of the results to only thread openers or only replies.
Maybe it could be a setting in an enhanced search.
2. It would also be nice if when you're in a category for example on this site 'Bugs' and you do a search it automatically defaults to search the 'Bugs' category only!
To stay in your example; What, if a poster reported a bug but selected another category for the entry? You'll not find this entry without changing the category (and: you have to know this mechanism!).
I think, it's reasonable to search for result in the selected category. But it is not reasonable to exclude valid results from the search because of their differing category. In my humble opinion it would be enough to order the results from the matching category to the top of the result list.
at the moment if I'm viewing the 'Bugs' category and do a search it gives me all categories and I need to then click 'Bugs' in the drop down menu and click search.
Yeah, that's a "feature" of the enhanced search and an ordered list of search results (as mentioned above) would make a change superfluous.
Trenne niemals Müll, denn er hat nur eine Silbe!