We have about 30 minutes to get from gate B89 to B29 in Denver. Any problem with time do you think?

You'll be fine if your flights are on time - I once had a 35 min connection from gate 24 to 79, and I got to the gate with time to spare; however, I'm not sure what delays can be like at DEN, as I've only flown through there twice, and both times my flights were on time.

Thank you. I know I can walk a mile in 20 minutes, but on the map it looks like quite a trek.

I've been thru UA terminal in DEN a number of times. You should be fine, as long as your flight into DEN is on time, or at best, only a few minutes late.

Keep in mind, they will hold a UA departure flight IF there is a fairly large number of passengers arriving on a UA flight that is running late. I've also had that experience.

I really don't see any big problems. Just walk fast (but there are shops and shops to peruse on that walk).

You won't have time to dawdle but you should be fine. You will already be airside on the same wing. It's tho long haul from check in to the gates that is the killer at DEN.