We can sort of do some of these with existing tools:

> * A way to filter the SF site to only see questions from users with a rep higher than x
> * A way to filter out questions if the user asking is unregistered
> * A way to filter out questions if the user has a rep less than 200 on SF but higher than 200 on SO


These are unlikely to ever appear as an official tool.  
The basic concept of Stack Exchange sites is that crap gets seen by a large number of people, declared to be crap, and closed.  If we allowed filtering by rep there would be a pile of crap from 1-rep accounts that nobody ever sees (except the 1-rep account holders who don't have the filter privilege).  

Basically this would make things **look** nicer for most of the site regulars in the 10k and 20k+ range, but the quality problem would get worse for everyone else (and our "% Answered" statistic would go completely to shit because nobody would be trawling through the muck to answer the genuinely good questions).

***What we can do is filter by question score*** -- Check out [the slightly improved Search documentation](http://serverfault.com/help/searching) for details.  
You can create and bookmark search queries to use as your Server Fault homepage.  Of course this relies on someone actually reviewing the questions in an unfiltered view **and upvoting the good ones / downvoting the lousy ones (again we're back to "The site works better when smart people help get rid of the crap).**

(That last part was bolded by Ward because - once again - the solution is MOAR Voting!)

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>A way to filter out questions with tags that are of no interest or I have no expertise in

We have [Ignored Tags](http://meta.stackexchange.com/questions/19173/what-do-favorite-tags-and-ignored-tags-do) for this. I suggest using the default "faded out" rather than the optional "completely hidden" mode, because you never know when you'll find something useful on a post tagged [tag:windows].

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> A way to combine, mix/match filters, and/or, etc.

The two tools we do have (Search and Ignored Tags) stack, so this is basically "combined by default".

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I know none of these are really optimal solutions, but they're at least a starting place.  
If additional search operators would be useful we can definitely propose them to the Stack Exchange team.