I still use it on occasion, although it's painful and I only do so if I have to. I did have some Aperture-edited images that I thought I'd continue to need Aperture for, but that's proving not to be so necessary, as modern image editing applications seem to produce better results with the original than I got with Aperture. Some of that is just that I have more presets, plugins, tools, etc in modern applications, and some is that I am just sorta re-seeing the image, but still: less need to even keep it on the machine. I already deleted tons out off it's library.
If you do continue to use it, even if you plan to never ever upgrade to new hardware or system software (good luck with that), have a plan B. Having dealt with old machines that died and then with the old software that could only run on systems that can no longer function on current Mac models, I can say it's a nightmare (a colleague who waited too long with tons of business documents in Appleworks eg).