At SAY Media we've decided to start using Google Apps. I'm super excited about this -- I've been advocating for it for a long time. I switched over today, and holy wow, I was not used to this. My workflow involves two major things: making copies of messages, and automatically BCC'ing myself. Neither of these works the same way in Gmail, but I finally figured it out.
Making copies of messages just doesn't happen in Gmail. Instead of five copies of a message being in five folders, you have one copy of the message and it's in a bunch of different labels. So when you delete it from one place, you delete it from everywhere. Un-labeling is what I want, instead. Figuring this out solved a bunch of my initial workflow issues. (Bonus tip: "sent mail" is really just a filter of all mail with my From address. Really, every filter/tag/folder/label is just a search on top of "All Mail".) So deleting a message anywhere will delete it everywhere.
Automatically BCCing myself isn't a feature available in the web UI. I was a little surprised at this but I wasn't going to go for the GreaseMonkey route. First I tried creating a filter for all messages matching me as the from address; I was going to tag them into the Inbox label, but that's not possible either. Eventually I found a really gross workaround: if the action is "Never mark as spam", that's equivalent to "Mark this into my Inbox". Hopefully that doesn't break.
With those modifications in place, I can go through my email the way I'm used to. I just need to remember to "archive" a message instead of "delete", and I'll be good to go.
ETA: Also, if I'm in the Trash, I can't just un-Trash something if I want to undelete but keep it archived. I have to assign it a label, then go back and remove that label. Ugh.