I'm a bit OCD with start screens - was the same with my iPhone where I only ever had a grid of 3x4 on the first screen so there was a gap (don't ask me why!).
With WP7, I have 4 x 2 above Pictures, and 4 x 2 underneath. I always have phone, messaging, people, twitter (Rowi), Personal email, work email, RSS (Weave) and IE in the top section for quick access, then Zune, Xbox Live, BBC News, Your Weather, Bingle maps, Wikipedia, Marketplace and Settings underneath.
When Mango lands, I'll combine the two email accounts leaving me with a spare "hotspot" slot above the Pictures "divider". Most of the time I'll probably have the new connectivity shortcuts app there to flip wifi on/off, but if I'm e.g. in London for the day I'll probably swap it out for London Travel.
Funnily enough, this is one of the many reasons why I dislike Android - you can't organise anything nearly as well. Widgets can be any shape/size, with no uniformity or consistent design to them, you can have widgets AND icons but the icons show no info, and it takes 7 screens to display the information I can see in one.
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