plastipunk, I don't think it works in the way in which Jag described. I could be wrong but from my experience it isn't like that.
I have got certs and sent them back in myself so I am speaking from experience. When I have taken certs out of my account, the shares are GONE from my account. There is no little side record or anything like that. If I had 100,000 shares and I got 90,000 in cert form sent to me, I'd have 10,000 left in my account and 90,000 sent to me in paper form. I could then take that 90,000 and deposit them to a different account at a completely different brokerage. So... it makes zero sense to me that I could call up the first brokerage and tell them to just "trust me" that I have the 90,000 shares and please sell them for me when at the same time I could sell those same 90,000 shares out of my other brokerage account. I'm nearly certain it doesn't work like this.
Instead, from my experience, you can't trade the stock you hold in certificate form until you deposit that stock in a brokerage account. If you live in a large town you could likely walk into a brokerage, setup an account, and give them the certificate. After some period of time (likely for verification purposes) you'd then be able to trade them like you would any other stock you would buy online. For me, I have Fed-Ex'd them overnight to E*Trade and then after about a week (it seems like it was about a week) they showed up in my account and I would have been able to sell the stock if I wanted.
So, yes, having your shares in certificate form in your kitchen cupboard (I'd recommend a fireproof safe though. LOL) will slow the process for you being able to instantly trade your stock like you can with your "electronic shares" in your account now. From my experience it is about a week or so BUT, if you are buying and holding then a week delay shouldn't matter :)
Don't take the above as gospel though as I may have just not realized I could call them up and sell something I didn't have. LOL But, at a minimum if Jag is correct, I would suspect you'd have to have a margin account with enough margin to cover the sale IF you failed to deliver... but I really can't see it working like that either. What I'd do, if your broker doesn't know, is call a different one (E*Trade maybe) and just ask them something like "Hey, if I have an account with you guys and have 100,000 shares in certificate form here at my house, at what point can you sell those shares for me and about how long does this process normally take?"