For the reasons explained above.
The conversion from 220 to pre-220 formats is not straightforward and in certain cases lossy, resulting in texture alignment bugs. This will also ruin one of the most brilliant Hammer features named "seamless texturing" (Alt+click).
"Brush primitives" used in some Q3 editors are also quite limited.
But, it is extremely easy to add 220-format support to any pre-220 compiler! Jackhammer comes along with 220-capable Q1 and Q2 compilers. Their source modifications will certainly be available. 

Here's why:
Say you cut up the floor into tris and then select 3 of these wedge brushes that share a vertex in the middle. Enter vertex mode--time to make a hill. In Hammer or Worldcraft you have to drag a selection box around that point to select all 3 verts from all 3 brushes. (okay 6 verts unless they're tetrahedrons(recommended!)) NOT SO IN JACKHAMMER!! :D Just click the vertex that's shared and TADA! all are selected. This is a huge time saver when working with tri-soup (trisoup? tri soup?) or anything really that requires multiple brushes in vertex edit.

Eat your heart out Valve. Jackhammer is already better and more stable than your precious Hammer with it's downdates and downgrades and hacktches. (see what I did there, I hate it when an update breaks something)

Puhshaw! Who needs displacements (or a displacement to brushes converter)? 

Is it possible to save your map as a .MAP file in jackhammer? 

only in map 220 format.
No way to save a generic map, because specific texture axis handling in Jackhammer. 

Is Jackhammer still in active development? If so, could you share any new features or changes planned in the next version? 

I'd be interested in this too. 

Ditto. 

>>Is Jackhammer still in active development?
Yes. In the next version there will be Quake3 support. With patches, realtime shader script rendition, wysiwyg shader editor, and so on.
And some other additions, e.g. fully functional Path Tool. 

If you understand Russian, you can monitor some progress here:
http://hlfx.ru/forum/forumdisplay.php?s=&forumid=35
And even download pre-release Linux-only versions. 

I'm only interested in the Quake 1 aspect of Jackhammer, but that's good to hear Jackhammer is still being worked on. You guys are doing terrific work with it. 

So cool, always wanted an editor for Quake 2/Quake 3 engine games with hammer-like interface.
But please, add the Alt-E (vertex scale) tool from hammer, it's a VERY useful feature.
Waiting for Q3 support! 

Is there a way to hide all entities? When i push the button "hide entities" it doesn't hide all entities
The monsters/lights still remain

And one more time, how to navigate through the level via built in camera, is there a way to place more than only ONE camera?! 

>>add the Alt-E (vertex scale) tool from hammer
It is already there, in 1.1.320. :)
>>When i push the button "hide entities"
Where is this button?
>>is there a way to place more than only ONE camera?!
Nope, sorry. 

but jackhammer menu is the same
http://www.imagebam.com/image/14e1d2346550899

multicam from hammer
http://www.imagebam.com/image/6f0f3a346551136

Nope, sorry.
it is very handy and useful feature 

>>but jackhammer menu is the same
Items means items, weapons, etc. :)
Well, you can hide all entities using Entity Report tool, by selecting all the list and hit "mark", and then "Hide selection".
At least, in JH.
>>it is very handy and useful feature
Yeah, I know. But not essential as many other features. Maybe, some day... 

That would have saved me about 45 minutes of extra mapping time...

Autosave. 

Autosave is already present. Version 1.1.320. 

And my apologies, but is version 1.1.320 not released yet? On the website the only available version to download is 1.0.155.

Do you plan on releasing this new version soon? 

http://hlfx.ru/forum/showthread.php?s=&threadid=4449
The reason it is not published on the website is that this is a Linux build only. There are still some minor bugs. 

I do look forward to the Windows version when it is ready. You guys are doing excellent work :) 

Is there a way to have spacebar move you around the 3D view and also allow you to pan around in the 2D views as in Hammer? I don't know if that's been added since. Also have some issues with it not registering spacebar is held down when attempting to move in 3D window and it clicking/selecting brushes instead which is a pain! 

I didn't try this when it got released and I now regret that. After watching Daz map on twitch yesterday I decided to try it out.

This editor is good. REALLY good.

I have a few things I'd like to see changed or improved but what there is already is outstanding. 

Except for this shit which seems to pop up with regularity:

Bad texture axes on face:
face point at (608 128 32)
face area = 512.000

Which brush is it? GUESS. 

are the numbers incorrect? because it sounds pretty specific. 

Coordinates are accurte, yes, but I'd rather know which specific brush was having the problem. The problem is that faces look fine in the editor, so I basically have to delete brushes in the area until I find the one it's talking about.

It happens when you use SHIFT+ALT+R_CLICK to copy textures and attributes to entire brushes. That feature leads to sadness.