I have five classes, but I am no way a pro. I have only just started my instances in Outland (not even Heroic yet) as a MBer. It was an eye opener that's for sure. I really learned how much I actually sucked as a MBer, lol.

That being said, I have both macros that have mixed spells for all classes and some for specific classes. Basically similar to what everyone else posted.

First, my main is a prot paladin. So, I have the standard single player hotkeys/macros for this toon.

For my other 4 toons (shaman, druid, priest, mage - currently all DPS until I switch my priest to Holy)
a) A DPS spam macro for my DPSers - I think I may make this into 2 macros, one for instances other for questing/trash. Currently using both /castrandom or /castsequence in the macros depending on the class. I am continually refining and trying to make these better.
b) Heal macros for each one of the five characters and others (PoH, /targettarget macro on both my shaman and priest bound to the same key)
c) utility macros - several of these, as each class obviously has unique spells - I think this is what you wanted to know, so for each unique spell I have (or will have) a hotkey (with or without a macro). For example, polymorph, shackle undead, psychic scream, ice block each have separate keys bound to them.

I use a G15 which has 18 programmable keys on the left side. Most are bound to this (atm).
I have 2 computers, each with separate keyboards and mice - I havent taken advantage of this yet (i.e., I could use the slave keyboard independently). However, for some spells I just click the mouse in the proper windows (e.g., rez).
I am a "PVE'er". PVP would be different or at least have more macros.

Also, many people run the healer (if you have one) as the main so they can reduce the micromanagement through hotkeys since the majority are likely to be healing macros. I don't think I would be talented enough to run a main healer with a tank slave.

Hope that helps a bit.

Cheers.