Just to share an experience with sharepoint 2007, been working with it for like 1 year, still a newbie.
My boss wanted to display some values: average, sum..etc, and he wanted that to look something like a KPI list. So I did use KPI list at first. He said "I dont like all those fields and I want the average of a column called activities and after that I want that value to be divided by another value which is in another list". so first, as far as I know, you cant add columns to a kpi list...well actually you can..but they wont display....of course my experience ( maybe they will show with a bit of code..I dont know), and I dont think that you could actually make some operations on a KPI list since you cant add more columns (again my experience...)so I was stuck.
I read on a forum about the amazing data view webpart and some tricks that you could do using sharepoint designer.
So first I did a Join between two list using sharepoint designer ( here a good guide how to do it http://blah.winsmarts.com/2007-10-Performing_joins_between_SharePoint_lists.aspx
thanks Sahil )
and then using a dataview webpart I started to play with the values of both lists, and I made a view like a kpi list as my boss wanted. Then He said "I want that to display only the values of the present months and all hte months before...since the column was showing only the number of month with a couple of tricks and using a condition I did it!. I was like "oh, its working!".
This is how one of the code lines look:
<xsl:if test="(@Title= 'Diciembre') and number(ddwrt:FormatDateTime(string(ddwrt:Today()),1033,'MM')) >= number(../../../Programa_de_Capacitacion/Rows/Row[@Mes_plan=12]/@Mes_plan)"><span><xsl:value-of select="sum(../../../Programa_de_Estudios/Rows/Row[@Mes_plan=12 and @No_x002e_eventos_real_x002f_mes>= 1]/@No_x002e_eventos_real_x002f_mes)"/></span></xsl:if>
And when I was about to show the results to my boss he said, "dont worry I used a spreedsheet on excel and I'll upload it on sharepoint"...duh!......waste of time.
Well actually I learned something new on sharepoint 2007 but well..I hate my boss...heh....I wonder if this method to join list and dataview to show stuff would still work on sharepoint 2010 or 2013...does anyone know?
Sorry about the long post and my english, but wanted to share. I kinda feel better now hehe.