How many versions of arduino have you got?

I've got a few versions of arduino on my pc and I'm probably wasting space but I bet I'm not the only one.
Just wondering what versions are best to keep. I believe there are incompatabilities with existing code for some older or newer versions.
At the moment I've got 21,22 and 23 and 1.0.3.
Are there any I haven't got I should have and which of these should I ditch.
Also is there a way to tell each version where it's sketchbook is and keep it. I've noticed that when I switch ide's I have to change the sketchbook back. Really annoying.

I have 1.0.5 and 1.5.5

I have been using 1.5.5 more and more.

0018, 1.0.5, and 1.5.5

I keep 0018 for firmware updates on my 3d printer

I’m using 1.0.5 for most everything robot related.

I keep 1.5.5 for when ever I start playing with my DUE.

 

I could probably try and do everything with 1.5.5, but I didn’t want to abandon a system and then find I needed it later (also laziness, lets not forget laziness :P), which is why I find this topic interesting as well.

I downloaded 1.5.6-r2 and it

I downloaded 1.5.6-r2 and it asked me to uninstall 1.0.5, so I did but it didn’t mind 1.0.3 or any of the others I had.

Heh, instead of getting rid

Heh, instead of getting rid of a couple versions I now have 3 extra lol.
As far as my second question regarding setting location of sketchbook in preferences sets it for all installed versions.
I think I may have been mistaken in believing I had to have a separate sketchbook for each version. It would get confusing remembering which sketchbook and ide you used for a particular project.
Does anyone have their own preference on organising their sketches.