First off, welcome aboard. Always nice to meet a new customer. :-)
On to the questions...
1. I'd handle this by making a "check that <foo> is back at work" action with a due date of Monday, and then assign it to their context.
(Arguably, this is a bit of a hack, since the person isn't actually required to complete the task. In practice, assigning a ton of stuff to a "self" context isn't helpful in my experience.)
Side note: some folks like to use a "Waiting For" context, but other folks leave the action assigned to a context then use the start and due date fields to control when an action shows up on the active task list.
Personally, I'd handle the "see if person is at work" task by assigning it to the context for the person. Have it start before work on Monday, and be due at some point that morning. I'd take a similar approach for the "email from Jane" action as well.
Your mileage may vary, but that works well for me.
Currently, there isn't an option for reminders separate from due dates/times, but I know we've got a request open for that in the development database. If you'd like to add your vote for that feature, send the
support ninjas an email and they can do so.
2. There is indeed a simpler way. :-) I'd suggest checking out the "Clipping material from other applications" topic under the help menu for the basics on the Clipping feature.
Once your clipping shortcut is set up, you'd just select the message in mail, hit the shortcut and then finish up the action in the quick entry window. (The advantage here is that the Quick Entry window doesn't make OmniFocus the frontmost application.)
Additional benefit: if you're using Mac OS 10.5 or 10.6, the clipped mail message includes a link which you can use to launch Mail.
3. Completed actions aren't removed from the database; they're just hidden. The simplest way to show them is by selecting
Perspectives -> All Items
and then using the toolbar search field to search for the items by name.
Hope this helps!