(Like the Tyranid page, this is also a re-typing. Unlike that page, this was written several days after the first try.)
In many ways Orks are the coolest race in 40K. What's interesting is that this is a recent development. Until just before we bought our figures, the Orks looked like silly cartoon characters and not like the tough-as-nails greenskins we know today. Unfortunately, they still haven't released new vehicles, so if you want to know how bad the Orks used to look, check out the drivers on the bikes and trukks. Eew. But thankfully the main Boyz forces have all been upgraded to look dead 'ard.
The Orks also have extremely cool fluff (that's non-rules "extras" for you non-40Kers). I love reading how Orks talk, since it's a sort of old-fashioned lower-class English. This doesn't extend to the many sad wannabe fan sites on the Internet which try to fake it and fail miserably.
The Orks have been around for a long time, so they've long since outgrown their fad phase that the new armies are going through, when all eyes turn to them, and then just as quickly they become boring and fall by the wayside.
That's not to say that the Orks aren't in the spotlight, though. Good ol' Ghazghkull Thraka is still a mighty force to be reckoned with, even after his embarassing defeats at the hands of Commissar Yarrick. There's always the chance that he'll finally manage to unite the clans, and like any good Warcraft player can tell you, that'll lead to an instant victory for the greenskins.
When they say that the Orks are the best for converting, they actually mean it. You don't have to worry about making your conversions look nice, you only have to glue on that extra gun, maybe throw on some extra bolts and cables, and it's all done. I've never actually done any Ork conversions, because apparently those slackers at GW forgot to send me the famous "bits box" they're always referring to.
One annoying thing about the Orks is that their units are so cheap. The way I see it though, this is only a problem for early collectors. Unlike what I first thought when I started playing, battles won't always keep getting bigger and bigger as you go along, because you only have time for about 1500 point battles. This means that you don't have to buy figures forever and ever, so you can get a 1500 point army and be done. Unfortunately until you get there life is harsh for a Warboss, since his only option is beefing up his existing models with lots of upgrades which are just going to make them targets for enemy shooting.
The other bad thing about Orks in the game is that they're a charging army, which means that you have to move every single model forward each turn, while your shooty opponent only rolls his dice for his guns and mows you down each turn. This can get pretty frustrating, especially when you run out of momentum before you reach the enemy lines.
But don't despair. The inherent coolness of the Orks outweighs any of these disadvantages. So if you ever feel discouraged on the battlefield just let out a mighty WAAAAAAAAGH and smash your opponent over the head with the main rulebook. Hey, there's gotta be a reason for how huge it is!