I am currently experimenting with an incubate list for items that I want to get to soon, but not right now. My lists for work had become too long and I realised a couple of weeks ago that some of the items just didn't have a high enough priority at the moment to be on my regular action lists. The question was where to put them so that I could be sure that they would be reviewed often enough. I had recently read a thread on the GTD Connect forums about incubating to "month X" and placing the list in the tickler to be reviewed at that point. This really made sense to me so I have given the idea a try from April to May. I made the "incubate" list in mid-April and placed it in my tickler for 1st May, with a reminder in outlook to check it on that day.
The list worked really well - I had much tidier and more focused actions for April that really helped me to engage with my lists (see also my post on coloured paper!) and could be certain that the items I had incubated would not be forgotten. When 1st May came round I brought out the list, scanned through it and put a couple of the items back onto my action lists. The rest stayed on the incubate list to be looked at in 3 weeks time and went back into the tickler (with the appropriate reminder).
This list is obviously a version of Someday/Maybe, but feels more active. I have always struggled a bit with the Someday/Maybe list. I can see its value and wish that I could utilise it better, but somehow I always feel slightly nervous about it for items that need to done at some point, just not now. I'm very happy to use it for items that I'd like to do, but don't actually matter if I don't get to them.
The incubate list is definitely the best route I have found so far to stay comfortable with that "not now but later" type of list.