Tumblr Saviour (based on a similar, much simpler script by bjornstar) allows you to control which posts do you want to see on your dashboard.

Do you have that nice blog you want to keep following that occasionally posts things you're uncomfortable with? Are all your friends fans of some show you don't like? Is there a person you really don't like, so you don't want to see anything regarding them ever again?

Tumblr Saviour can take care of it for you.

• Post black- (removal), gray- (spoiler) and white- (exclusions) listing.
• It can filter notifications & notes as well.
• Decide what to do with recommended & sponsored posts.
• Starts filtering posts as soon as the page starts loading - now it's hard to notice removed posts were even there!
• Fully configurable via configuration panel (check Greasemonkey menu).
• Doesn't break Tumblr keyboard navigation.
• Tweaks post styles to make sure missing posts are unnoticeable.
• Processed items are marked with data-tumblr-saviour-status and data-tumblr-saviour-reason attributes - now you can check why post has been processed in certain way.