Sometimes after I copy-paste code snippets from web page into emacs buffer I get text with superfluous blank lines delimiting code.
Marking region and running M-x flush-lines RET ^$ RET quickly makes it better by removing those pesky blank lines. This is, of course, makes sense only if pasted code doesn’t contain blank lines you want to preserve.
Update:
You may need to use something more complex than simple ^$ (something like ^\W*$ as regexp) if “blank” line contains some whitespace characters.
Example before:
-export([test1/0,
test2/0,
test3/0,
double/1]).
After marking region and applying M-x flush-lines RET ^\W*$ RET (in your case just ^$ may be sufficient):
-export([test1/0,
test2/0,
test3/0,
double/1]).
Ruslan's Blog 
There’s also
M-x delete-blank-lines RET.
Posted by hober | October 22, 2007, 6:31 pmYes, that one is useful on its own. It’s just that M-x flush-lines RET ^$ RET will work on region like:
text1
_blank_line_
text2
_blank_line_
text3
producing:
text1
text2
text3
while C-x C-o works only on consequent blank lines.
Posted by Ruslan Spivak | October 22, 2007, 7:34 pmGive M-x delete-trailing-whitespace RET a go too ;)
Posted by Jesper | February 20, 2008, 9:04 am