While I've been to the Redmond campus of Microsoft, where I now work full-time, 5 times already this year, it's not the same as actually working here.
I'm finding that I have to make an effort to get outside the building and get some fresh air every day. The good news is almost everyone at Microsoft has a "real" office with a door. The not-quite-as-good-news is that unless you've been around the company for a number of years your office has no windows (the kind where you see outside...). So going outside has the added benefit of letting you stay connected with the real world!
I feel like I'm starting to get a handle on what exactly I now do for a living... each Technical Evangelists job is slightly different depending on the technologies and customers involved.
The best news of all is that I'm eager to come to work in the morning and satisfied that I've done some good when I go home at night... which is exactly what I signed up for!