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I have 6 on my iPhone,

Phone, SMS, Mail, Calendar, ipod and safari.

It's a little cramped, but I hate scrolling to get these most important functions.

They should have made it originally so that you can add more, and if you do, they shrink a little.
 
Since my iPad is my primary computer I have the following in my dock:

Email
Safari
Calendar
Contacts
Goodreader
Settings
 
I have: Mail, Safari, Videos, iPod, Photos and Settings. I then have the most important or favorite apps on the home page, followed by other pages with apps organized according to function/category. Works for me!
 
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