Ken,
I use the Hyper memories and they are very useful. There is a good write-up on what they are and how to use them. The Yaesu manual is weak in this area. The purpose is similar to what Eric says about the presets but it is more than that.
Basically, each of the 5 Hyper memories is like a setting for a different radio configuration. Almost every radio setting can be configured the way you want it for a specific purpose and configured for one of the HMs (or all 5 of the HMs)
I'll give you a couple of examples:
HM1- Set for your configuration while in town. Local repeaters, custom power setting per mem location, mem alpha code, local simplex that RS uses, etc.
HM2 - Set for your travel mode. Simplex frequencies, state police freqs, FRS/GMRS, etc.
HM3 - Set for your state-wide repeater network.
HM4 - Set for your off-road club events. Your RS simplex freq, 145.52, maybe the closest repeater that would have coverage in the area where you have the event.
When you press the HM button the radio will automatically go into scan mode if that is the way you set up the HM, or into VFO mode, or into Memory mode.
The FTB7800 software gives you a great visual into the workings of the radio and it has a pretty good explanation of the Hyper Memories. It takes some time and tinkering to get it set up the way you want it but, like anything else, the effort will pay off in giving you more flexibility in using the radio.
I tweak mine about every 2 months and would do it more often if the radio wasn't mounted under the front seat.
Here are some links:
Hypermemories
http://f1.grp.yahoofs.com/v1/MDDfR_...W9YwecITpl_A/Yaesu_FT-7800R_Hypermemories.pdf
http://f1.grp.yahoofs.com/v1/MDDfR-...BvyJI-zydT5A/Hyper Memory thing on the FT.doc
-B-