90 minute boils are usually done to drive off DMS when using a lot of pilsner malt (all grain brewing).
you would get some additional hop utilization from a longer boil as well but I don't think too many people are doing that.
A full boil has better hop utilization due to not having a wickedly high gravity wort. You can do exactly the same thing in a partial boil by following the late extract addition method.
Yes, you need extra wort to end up with 5gallons after the boil. I can lose up to 2 gallons an hour if I use my KAB5 burner.
And you do pretty much need a chiller of some type to deal with 5 gallons of 200 degree wort, although several people have tried 'no chill' brewing with success.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10