Just to toss in $0.02, for me it all depends on what I want to run. I do keep some copies of Warp 3 around, I also have Warp 4 and eCS.
If I'm looking to run the more up to date stuff that is available for OS/2 then no doubt I'll use my eCS desktop.
However for some stuff, I find that Warp 3 does quite well.
As an example, I have a machine set up as a print / file / web / ftp / MySQL / time / plus a few other things server. All of that stuff runs fine under Warp 3, the computer I have it running on runs fine on Warp 3, and since I have 6 Warp 3 licenses kicking around I didn't really see a need to purchase an eCS license for that computer.
Another Warp 3 box I have running is mainly being used for its DOS support. Its got a custom hardware card in it which came out around 15 or so years ago and only has DOS software to make it work (its actually at a radio station I do support for). Originally the software was never written to be TCP/IP aware (although it will take commands via a serial port) I found that by using the DOS support in OS/2 and writing a few REXX scripts, I can control the system over the internet. While I'm sure I could make it work on Warp 4 or eCS, it runs just as well on Warp 3's dos support. Note that I probably could have achieved the same result under Linux, although it likely would have taken a little more work and troubleshooting to get working.
I've also got an older Compaq laptop (a P2, about 15 years old) that I've used as a demo of what it was like using laptops / computers 15 years ago. Its got Warp 3 and Win98 on a dual-boot (boot manager!) basis.
Even though it is old, Warp 3 can still have a place. Although I agree that some of the memory limitations it has do limit what newer apps can be made to run on it.
And just for full disclosure, I also use Linux and Windows (XP and 7) on a regular basis.