You may have noticed that some Joinees are referred to as Silver, Gold, Platinum or Diamond Joinees. Also, some have letters after their names (for example "GA"). None of these things matter. They're just for fun.
We've called them ranks here, because we couldn't think of anything else, but they're more like badges of honour, and certainly don't give the Joinees in question any more authority over the collective. To try to explain them individually:
Silver Joinees have done something cool for the cause, like an extra special RAoK or recruiting a bunch of people (5 is reputed to be the norm for silvering). Being around Danny when he's had a couple of drinks also helps — apparently he once said the whole of Edinburgh was Silver on the basis that "Edinburgh's great!"Gold Joinees have done something even more special, like organised large meets, done stupendously great RAoKs or embarrassed themselves publicly for charity. Having been around for ages helps too, although it's not unheard of for people to get Golded the day they Join!
Platinum Joinees are very established, awesome joinees. It started off with just Joinee Whitby, but since then a few others have been promoted. First were Platinum Joinee Fowler and Platinum Joinee Rufous, and there have been a few more since then.
Diamond Joinees have put up with all sorts or be superstars! That's not strictly the criteria... but three of the handful of Diamond Joinees have at some time run the Joinee forum. They are Diamond Joinee Whitby, Diamond Joinee Matt Fowler, and Diamond Joinee Collins. There was also a special Diamond Day in February 2006 during which all Joinees were "entitled" to call themselves Diamond. At Karmageddon 7 the previously Platinum Joinee Mum White's promotion to diamond was announced to much applause!
The most important thing to remember about the "ranks" is that they're not important nor particularly "official" in any meaningful way. One should never do things to get silvered / golded / platinumed, because for one thing you'll likely be disappointed as Danny doesn't hear absolutely everything that goes on, and for another you'll get far more satisfaction out of something you've done for yourself. However, if you reckon you or someone you know deserves silvering or golding, why not drop Danny an e-mail and explain why?
There are a few others that slip through the net. There are those who get multiple Silver stars (often when Danny has forgotten he's Silvered someone before), or the Double Pink Joinee, who was Double Pinked after some drinking at the expense of the BBC. Most promotions are indeed the fault of alcohol. See Other Stars for more details.