Note: While writing this I realized it is a feature needed to work around a bug.
Following the lead of Cedric and Krzysztof, I have some gmail requests too. When addressing a mail to someone with multiple addresses, it should remember the address I used most recently, and put it at the top of the hint list.
Many of my contact use mail redirection services so their address is something like "Bob [at] myVanityDomain [dot] com" which is forwarded "poluted.namepace.random.string [at] gmail [dot] com." (Here's the bug:) Connecting to this person in google talk required (not sure if it still does) the gmail address to be the primary address, or the invitation just did not work out. So now when I start typing bob's name, the gmail address appears first. I want a way for it to remember to use the other address instead.
As to my comment on Cedric's blog, I discovered that if I add something like "familyMember" into the notes of an email address, I can view my contacts, and then search for "familyMember" to get a list of all the people in my address book who are family members for group emails, but I'm still waiting for address groups or tags or something to make group mail easier.
One last thing. It does not appear to be possible to archive "sent" items. They are either sent, or deleted. Which mean that either you allow your sent folder to collect clutter, or you delete them all together.