In general, you cannot cast more than one spell with a single click of a macro. Most spells and some items trigger the global cooldown (GCD) which keeps you from taking too many actions at once. Even if a spell fails to cast, if it would trigger the GCD, it prevents subsequent /casts in the macro from running. This was not the case prior to patch 2.0 which is why you may still come across macros like the following:
/cast Overpower
/cast Execute
/cast Mortal Strike
/cast Sunder ArmorMacros like this do not work anymore. As soon as Overpower fails to cast, the game will block all the other spells from casting as well, even though the GCD is not actually triggered.

There is a bit of good news, though. Certain spells can actually be cast at the same time in a single macro. Any spell that is instant and does not trigger the GCD can be followed by another cast ("Next Melee" abilities like Heroic Strike fall under this category too). The spell's tooltip will tell you if it's instant, but you have to use the spell (or check a spell database site like thottbot.com) to know if it triggers the GCD. Example:
/use Talisman of Ephemeral Power
/cast Arcane Power
/cast Presence of Mind
/cast Pyroblast
Humm I don't know if using

/click
/click
/click

to get around the /cast limitation is umm.. At any rate thats a nerf waiting to happen and bad practice to get into.

Why would two /castrandom or /castsequence be usable in macros? Once there is ANY failure to cast a spell that triggers the GCD that failure will stop the WHOLE macro (including the 2nd /castsequence or /castrandom) correct?

And if your first one dosn't fail then why do you need to put in the 2nd anyway?

So if line 1 fails you dont get to line 2, if line one 1 works you dont get to line 2. Thus you never get to line 2.

Humm so the game checks for a failure with /cast but dosn't with /click, /castrandom or /castsequence? Meaning you can just use any of those three instead of /cast? ... well pffttt

/castrandom Flame Shock,
/castrandom Lightning Bolt,
/castrandom Fire Nova Totem,

Well ...