If by idea sheet you mean like a notebook or just a word file to dump ideas I have, then yes, I do that. I have dozens of notebooks littered with ideas I have throughout the day. I almost always take a notebook with me anywhere I go in case I get an idea. Also I used Brandon Sanderon's idea (not completely his idea, but I took it anyway) or opening a file called "Cool Stuff I Want to Use Later" and I just dump whatever ideas I come up with there. It can be character ideas, a plot point, an image I like, ramblings, quotations, whatever. I find it quite useful to stave off Creative ADD because I'm able to put down ideas I'm interested in writing about while still keeping my focus on my current WIP.
Back when handwritten notes on paper were still an option for me, I had a notebook where I'd write, doodle etc about any idea that came to me.
Today, I have file(s) I call 'Ideabook' where I detail any idea I think needs a bit of context, and I often will just put down a title or sentence in a Scrivener document where I start most of my stories.
But, for me, and this is probably very specific to me.... I find that writing down stuff has the opposite effect of what I'd expect. It off-loads the idea out of my head, thus making it static, archived. The problem I have with archived stuff is... I would have to actively review (read) all of the stuff I write down all day to re-activate the idea. For various reasons, re-reading stuff already written has always been something that requires a lot of effort for me.
So today, if I am actively working on something I sometimes will NOT write down ideas, but rather keep them in my head, active and brewing. That means that once I actually write (or otherwise create) the original idea might not have survived... but it may have evolved, been integrated, mutated, refined.
I've also started to do something similar with actual written notes lately: I write them in the knowledge that I will likely never revirew them. More like finger-practicse etc. Once I do start to write the actual story, I usually don't consult my notes, but rather just re-write everything. It seems that having written it once before, the new version comes out more refined.
Sometimes, when I DO consult my own notes - this may be months or years after taking them - I am always surprised at them, thinking 'darn who worte this? What?Me?' - it's always fun to see where my mind was and compare it to where it is now.
I have a Word file with a table in it, where I can put in the idea, whether it's a character, plot or setting idea (with secondary categories like character relationship, setting - magic system, plot - ending, etc), and any stories where the idea has been used so I can keep track of it and avoid using the same idea more than once in something that reaches completion and publication.
I have a notebook with handwritten notes and synopsis in it, which I then transcribe to my Google Drive / Wiki pages. I tend to remember things best when I've handwritten them, so doing my initial brainstorming through notepad helps me to retain it, but the online storage helps me to organise it and quickly refer to it later.
I also have a miscellaneous idea note on my iPod where I write down any random thing that comes to mind, be it a scene in my head, or miscellaneous dialogue or whatever. It's very eerie how often those things just slide into place for the story.
I use Evernote to write something new across my iPod and laptop efficiently. It also houses all the grammatical details of my language-in-progress.
Edit: I also use Apps like Total Recall to make mindmaps and such. They help when I'm lookin at the plot and considering all the variables, but also are useful for putting new ideas into place.