Since I've hit 80 and starting to face gear choices again, I thought I'd do a noob's guide to the latest hunter DPS spreadsheet. It takes some setting up, and may seem overwhelming for someone who hasn't seen it before, but trust me - it's worth it!
I've written an introduction to the basics below; if you want to use the more advanced functions (shot rotations etc) you can find more info on the Elitist Jerks forums.
Guide to setting up the WotLK Hunter DPS Spreadsheet
1. Pick a day when the official WoW armoury is working, and you can see your character info.
2. Download the spreadsheet from the EJ forums at http://elitistjerks.com/f74/t30710-wotlk_dps_spreadsheet/ (note that this *used* to be called "Cheeky's DPS Spreadsheet", and was taken over by Shandara)
3. Overview Tab
Change the character name, server, and server set (US or EU) to your own.
Choose a name for your profile(s) (eg. "Phyllixia raiding", "Phyllixia PvP").
Pick your gathering skill (either Mining or Skinning, if you take them).
Pick your glyphs
4. Gear Tab
Scroll to the right and click on "Load Gear from Armoury". Make sure that it's the correct character name and realm.
Check your race is the correct one.
Your gear should have loaded - check that it's all the correct gear (sometimes it will miss something, or the item hasn't been put into the database, or you logged out in your Winter's Veil outfit etc)
5. Custom Gear Tab
If one of your items isn't in the database, or you want to create your own item, input the stats here. You can then go back to the Gear tab and select "Custom" in the appropriate slot.
6. Talents Tab
Click "Read from Armoury", again making sure it's the correct spec when it loads.
On the right is pre-loaded talent specs, which you can use and customize in the Overview tab if you often change specs (eg. for PvP and Raiding)
7. Buffs Tab
Pick a buff profile (none or raiding)
8. Pet Tab
Pick your pet and their talents.
9. Go back to the Gear tab, and click "Save Profile". This will now save your current gear (as well as your spec/pet/glyphs etc) as a default set. Whenever you get a new piece of gear and you want to know if it's an upgrade, compare the "Total DPS" at the top of the Gear tab with your old and new item. If you forget which items you've switched in, you can click "Load Profile" to go back to your original default.
10. Whenver you change something for good (eg. you get a new piece of gear, or you changed glyphs), remember to click "Save Profile" so it saves it as your new default.
11. Gear Planner Tab
If you're looking for where you can get upgrades, check out this tab. It highlights the item you have equipped, and shows you the top 10 items per slot in terms of raw DPS.
Now go forth and DPS!