Had a little very-mini-tour to Detroit with my girlfriend last summer! We took the train from Montreal to London, ON, and biked to Windsor to cross.
The border crossing was a little less than straightforward, but after tracking down a cabbie with a passport (make sure you ask on the phone!) we were able to cross both by stuffing our bikes and gear into taxis. On the way into the US we got a van cab, but on the way back (given that the selection of passport-laden taxi drivers at 6am on a Sunday is limited) we were forced to stuff our gear into a tiny yellow cab. Had to pull both the wheels off of both of our bikes, but we got where we were going
We stayed for a little less than a week with a really gracious couchsurfing host on Grand Boulevard and explored a bit using that as our base. The state of the city was a little shocking at first- I grew up somewhere where nobody locks their doors, and this is a place where you need to talk to someone behind bulletproof glass to buy a bag of chips! But once we got the 'Detroit eyes' everything seemed less threatening. Most people are super friendly as soon as you talk to them, and as long as you don't flaunt your nice bike at a liquor store late on a friday night you're totally fine.
The traffic is super relaxed in most places thanks to the relatively few cars on the road in a city that was built to accommodate a whole lot of them. Downtown is clean and safe. The stark contrast between the neighbourhood-turned-fields where we were staying and the sparkling crystal palace of the GM headquarters was pretty incredible. In any case- we were fine locking our bikes up for a couple of hours to eat dinner. The road layout makes no sense, so if you're used to square blocks prepare to spend a lot of time trying not to look confused.
If you have time to explore the area, the Waterfront, Dequindre cut & Belle Isle is a fun ride.. check out the abandoned zoo! Also take a spin through the Heidelberg Project. Super weird, unforgettable place. We even biked out to Zug Island to see if we could hear the infamous 'Windsor Hum'. No dice, but we passed some really incredible abandoned buildings along the way- The massive (open for tours, but not when we passed) Fort Wayne and the former ferry dock to Boblo Island, a (you guessed it) abandoned theme park on an island.. in Ontario.
Be safe, but be open, and Detroit is a really cool experience. Don't just bike through at top speed! I'd go back to explore more in a second. When that bridge finally opens to bikes I'll have my excuse!