boot up processes (questioning)

[René]

hello all
have a nice 2006.
today i did some work on boot-up processes (cause i complained about the  
loong booting time earlier).
i did use the instructions on:
http://ubuntuforums.org/showthread.php?t=89491
with some of the processes i am pretty unclear what to do.
can anybody help to explain, if i 'need' as a 'normal' one of the  
following processes:

1. dns-clean (one needs it for ppp. but also for eth0 ??)
2. evms (this one is only related to logical partitions, right?)
3. lvm (we need this one for all harddisks anyway? or is it also only  
related to logical partitions?)
4. libdevmap$ (do not know what is this at all !)
5. rsync (also used for encrypted file transfer, at least thats what i got  
to read somewhere. when do i 'need' that one?)
6. postfix (it is used for email, but do i need it with clients like  
Thunderbird?)

that would be fine if some people would answer.
many thanks.
René