I'm not sure whether to post this in the commuting or touring section, but...
I just ordered a Surly Disc Trucker as a dual commuter/tourer. I've already bought or picked out most of the accessories (fenders, lights, panniers, pedals, pump etc...) except racks. I had originally thought the Surly Nice Racks would be good, but after reading on this forum and talking with a couple guys at my LBS have decided to look at something else. I'm leaning Tubus (probably the Logo) for the rear and am trying to decide which front to get, though I've heard great things about the Tara and would like a rack with a connection from left to right side for stability.
For commuting to work and touring, I'll probably only need the lowrider mounts for my new waterproof panniers, maybe a light bag on the rear top platform when camping. However for around town errand-running, picnic-ing, farmers market runs, I think I would want larger platforms for front/rear baskets (?), coolers, and Kubb sets.
So, my question for you is: how useful and necessary are top platforms for your around town use? The Logo has a much smaller platform than the Surly or Tubus Cargo, but my size 13 (48) feet probably want the extra heel clearance it offers panniers. I'll probably get a set of open-topped market panniers (like the Banjo Brothers ones), so maybe I don't need platforms front or rear.
My old commuter when I was in school was a low-end mountain bike with a rack and trunk bag, so I have no experience with more sophisticated systems, but I didn't really like having to carry a messenger bag in addition to what was on my bike.