"Falsecarding", or drawing in a deceptive manner, is a key skill in 5CD. Other common situations are drawing 2 to a pair (usually keeping an ace as a kicker) and standing pat with two pair (or worse). I also usually draw one to pat quads because I want to improve my kicker [img]/images/graemlins/laugh.gif[/img]
You are right in that you will improve your chance of improving your hand by drawing 2 rather than 1. According to SuperSystem, it is 10.75 to 1 to improve three of a kind with a kicker to a better hand (boat or quads), while it is 8.65 to 1 to improve three of a kind w/o a kicker to a full house or better. I don't remember and don't feel like grinding it out, but I think your chance of filling up is less wehn drawing 2 but that the improved chance of making quads more than compensates.
We "falsecard" in draw for many reasons. Sometimes we do it to get action after the draw, sometimes we do it to "freeze" the opponent and hopefully get a free showdown, sometimes it is because we plan on bluffing and hope he'll throw his hand away.
If you plan on "falsecarding", you need to mix it up. I've played against lots of people who always hide trips by drawing 1 and they only draw 2 when keeping a kicker with a pair.
I'm not sure if you are playing live or online. If you are playing limit ring games online (at Paradise or PokerRoom), you should read this:
Online Draw Article
I've heard Mike Wiesenberg is working on an article for pot-limit draw cash games, which is played at 24h or PokerRoom.