Remember this though, gem/enchant for strength, reforge for hit/expertise. This is because gems and enchants are pretty expensive, and as you get more gear it will be easier to hit your Hit/Expertise caps. If you are hit/expertise capped, and you can still reforge more gear, reforge any crit/haste into Mastery. The new mastery bonus is awesome, and is our best stat to stack after strength which you can't reforge into.
Also, this is my rule, but I don't know if people have similar rules. Don't gem/enchant anything below ilvl 346 gear. Once you are doing heroics, you will be replacing that gear very quickly, and you will be wasting that money for a slight damage increase. That slight damage increase is useful when doing raids, but for heroics it won't make or break the run.
Heh. If your experience is anything like mine you'll likely be hard-pressed to avoid hitcapping through gear alone and be actively reforging away from it. I think I was at about 11%, even without a hit trinket...
My rule for gemming/enchanting is, once you get to gear that you'll be grouping with for endgame normals (325 blues or higher, basically), use a cheap green-quality cut in a non-primary color (i.e. purple str/hit for a blue slot, orange str/mast for a yellow). These should be real close to the 9g vendor price (for real bargain-basement, Wrath greens should be on the order of 1g). Similarly for enchants - there are some scrolls commonly used for leveling that require very cheap and/or non-endgame mats and are often dumped on the AH en masse. While they often aren't perfect - raw attack power and the like - they cost practically nothing. That way, when a stranger inspects me, my gear practically shouts "I'm conscientious, but I'm not stupid", and they hopefully don't initiate a vote-kick in the doorway like they might if they saw empty sockets.