A good example of this isa commit by acydBurn, which included 12 new files for a total of 4866 lines of code, Obviosly he didn't write all those lines of code in one day, so he must of had it in his local respository. And he didn't feel that it was ready to be commited until now. And in reality the acp.php file (whic i assume is going to be called) is not commited yet so those commits aren't functional yet either, but his reasons for summiting it now was so no one goes and waste their time editing files in adm/ when that directory is not useful anymore, since all the admin functions are moved to the new module system.
Not necessarly, if you look at the pattern of the commits, its very clear (at least to me) that they are very well setup as to who does what.it is practilcally impossible (not to mention inadvisable) to have significant ammounts on uncommited code when the nunmber of developers actualy justifies the use of the word "team".
for example; a great deal of grahamje's commits are for the MCP (Moderator control panel) and acydBurn's commits are mostly all ACP (Administrator control panel). So you can rest asure that at some point they got together and said, ok you work on this part, and ill work on this other one. So if anyone developer has some code that for some reason or other he doesn't want to commit now, then he will have the assurance that is not going to break the other's code if he doesn't, because their each working on separte parts to begin with.