Flush DNS cache

In Terminal, type:

lookupd -flushcache

Change Default Screen Capture Format in OS X

Enter the following into Terminal:

defaults write com.apple.screencapture type *format*

In place of *format* in the above put any of the following, depending on your preference:

jpg
pdf
tif
png - this is the default

(There may be others. Feel free to add these to the comments.)