It's tough to fit a trip to Speeds' into a work day, but today I finally created an excuse to be somewhere near Newmarket Square in the middle of a weekday.
I agree with those who have said that Speed's is impossible to describe. To really understand it you need to go. Also, there are plenty thorough descriptions here of the massive hot dogs basted with barbecue sauce, so I won't add another.
I loved it! I had mine with mustard and onions. The only thing I found odd (and oddly enjoyed) was the subtle taste of gasoline (lighter fluid?) that may have been on the hot dog but seemed to be coming from the bun. Any other experiences with that type of taste there? It may have been the way he smokes the buns on the charcoal grill. Whatever it was, it was good.