Better default toolbar setting

[Stefan Monov]

> > An alternative is to decrease the checking interval. What's wrong with
> > that?
> Well, usually one wouldn't change the check interval to 30 seconds or 1
> minute just because he /sometimes/ wants to retrieve messages instantly.
Yes, one wouldn't *change* it. But they can set it to 1 minute one day and 
forget about it. Decreasing the interval doesn't hurt anything but bandwidth, 
while increasing the interval hurts (by making the "get mail" toolbutton 
necessary by default).

> Another case where forced
> checks make sense is in mobile use, when one just wants to check for new
> mails and do nothing else, turn on notebook, check mail, shutdown.
KMail has a "Check on startup" option.

> Also, you make a lot of bold claims what people do how often, I wonder if
> that is backed up by any data or just guessing.
Guessing, and hoping someone will correct me with reliable statistics.