Q:

How fast is travel in the Ethereal Plane?

How fast is travel in the Ethereal Plane?  It's all sort of flat and ghostly (perhaps ethereal, even).  Tactical movement seems to be normal.  But is long distance travel any different or faster?

A:

Border Ethereal - Same as Material Plane (possibly slightly faster)
There is nothing in the rules that suggests that moving 5 ft in the Border Ethereal would move you any more or less than 5 ft with respect to the Material Plane. Thus, RAW, movement speeds should be assumed to be the same relative to one another.
However:

Solid objects on the overlapped plane don't hamper the movement of a creature in the Border Ethereal.

That could translate into slightly faster travel times given that the traveling creature would only have to avoid magical effects and living beings. But they could walk through houses and possibly even physical features like mountains without any issue. The amount, if any, of time saved by this would depend on the terrain and objects in the way, how long it would take in the other plane normally, and how far you are attempting to travel.
Using this method it can be possible, using etherealness for example, to travel to the Border Ethereal from the Material Plane. Then, travel in the Border Ethereal for some time (using the ability to travel through objects and such) and then returning to the Material Plane in the new place (potentially faster than moving there normally in the Material Plane alone).
Deep Ethereal - 1d10 x 10 hours for Interplanar travel

Traveling through the Deep Ethereal to journey from one plane to another is unlike physical travel. Distance is meaningless, so although travelers feel as if they can move by a simple act of will, it's impossible to measure speed and hard to track the passage of time. A trip between planes through the Deep Ethereal takes 1d10 x 10 hours, regardless of the origin and destination. In combat, however, creatures are considered to move at their normal speeds.

If you want to travel to another plane, then it will take you 1d10 hours to get there regardless of the distance to that plane. If it would have taken you longer to get there by some other route you have saved time. Otherwise it is the same or slower.
And this isn't even counting the ever-present danger of the Ether Cyclone:

An ether cyclone is a serpentine column that spins through the plane.
[...] The most common effect of an ether cyclone is to extend the
duration of a journey. Each character in a group traveling together
must make a DC 15 Charisma saving throw. If at least half the group
succeeds, travel is delayed by 1d10 hours. Otherwise, the journey's
travel time is doubled.

The Ether Cyclone can make travel much slower if it is encountered, increasing the travel time significantly.
Note, if you are trying to use the Deep Ethereal to move to another place on the plane you just came from it is unclear if or how that would work and how long it would take if it did. It seems likely that journeying through the Deep Ethereal would not get you back to the plane you came from at all and thus would not be useful for that purpose.

A:

It depends on how far you want to go
Creatures move at their normal speeds, unless you're traveling across planes (DMG 49): 

Traveling through the Deep Ethereal to journey from one plane to another is unlike physical travel. Distance is meaningless, so although travelers feel as if they can move by a simple act of will, it's impossible to measure speed and hard to track the passage of time. A trip between planes through the Deep Ethereal takes 1d10 x 10 hours, regardless of the origin and destination. In combat, however, creatures are considered to move at their normal speeds.

Given that you can pass through normal obstacles, you might be able to take a more direct route, but that benefit is going to be highly situational--you could bypass a mountain, but you won't get much of a benefit on a plain.
However, the presence of Ether Cyclones could dramatically extend or divert your journey, especially if you're spending a lot of time there (DMG 49): 

An ether cyclone is a serpentine column that spins through the plane. ... The most common effect of an ether cyclone is to extend the duration of a journey. Each character in a group traveling together must make a DC 15 Charisma
  saving throw. If at least half the group succeeds, travel is delayed by 1d10 hours. Otherwise, the journey's travel time is doubled. 

