=IF(OR([Status]="Planned",[Status]="Writing"),"5","30")
Does not really do what you might think, it does (in human language):
IF Status IS "Planned" OR "Writing" THEN 5 ELSE 30
You can accept Bhaskar answer, so he receives the points..
Reformatted it reads better (and cou can copy/paste it like this, SharePoint will ignore linebreaks and redundant spaces, I usually prepare a Formula in Notepad)
=IF([Status]="planned" , "5" ,IF([Status]="writing" , "30" ,IF([Status]="technical review" , "50" ) ) )
Couple of notes:
SharePoint only allows for 7 nested IF statements; you have to rework your formula if you need more nested checks.
The last IF has no ELSE clause, valid coding, but be aware SharePoint will make that a (default) FALSE value (for any status not mentioned in the IFs)
Update re: comments
You can not nest more than 7 levels deep
So you have to built Formulas like:
IF ( OR( 1 , 2 , 3 , 4 , 5 , 6 ) , IF ( 1 , Do One , IF ( 2 , Do Two ... , IF ( 7 , Do Seven , IF( 8 , Do Eight ...