A lot of people seem to be poopooing the changes as far as they pertain to the Marksmanship Spec. So as an avid Marks hunter(and my guilds Hunter Lead) I have been doing some testing on the 4.0.1 PTR this morning since my main arrived early on the test realm. (after poking around last night with a new toon to get used to the focus mechanic.)
A lot of people seem to think that MM's future is in jeopardy for various reasons but let me assure you it is not. Your previous play style with which you've grown accustomed to however is. Gone are the days of macroing a dozen or so off-globals to all of your shots. Here are some important changes to your shot priority.
Kill Command: Has a short cooldown and is on global, and is back to its old form. It's now a pop it when you got it cooldown shot.
Aimed Shot: Will be your major dps cannon, but you will be working around the Master Marksman talent to use it in a raid situation, which has a 60% chance to gain a stack and at 5 stacks it is replaced with a buff called "Fire!" (your aimed shot on your action bar will also light up in a very conspicuous manner.) Fire! reduces the cast time and focus cost of your next aimed shot by 100% (it lasts 10 seconds). Because it rolls from one buff to another, unlike maelstrom weapon you can't take advantage of a partial stack of master marksman in any way. One thing you will have to learn is not tapping aimed shot during your dps rotation unless Fire! is up.
Arcane Shot: You would think that the removal of armor penetration would make this a more desirable shot to put back into your rotation but it is not. Keep Arcane shot kicked to the curb. In cataclysm raiding when Aspect of the Fox is available you will likely not feel compelled to hit Arcane shot either.
Chimera Shot: This shots role becomes a little different. The secondary shot from Serpent sting is gone. I tried it with the improved Serpent Sting talent (serpent sting now does instant damage) but it does not in fact proc any instant damage when serpent sting is refreshed. Also the lack of the secondary shot is a bit of a nerf to our burst damage(ontop of the fact that aimed is no longer available for trash, the duration of master marksman is too short to really carry it on between targets) and makes Glyph of Serpent Sting completely useless to MM. It does however still do a massive amount of damage and should be fired every time it's up. The self heals are small but are likely there to give marksmanship improved continuity while grinding should you choose to use this spec.
Silencing Shot: No longer deals damage so it becomes a pick and choose talent based upon the availability of other interrupts for your guild runs.
Pet Suggestions and raid buffage: Your wolf pet now provides the 5% crit buff, which is good. However I would also recommend getting a Hyena as well for the 30% bleed debuff, which is often missing in 10 man groups and is probably still worth a good portion of overall damage. I do believe there are a few new sources of the 5% crit buff which could render the wolf somewhat obsolete. Trueshot Aura does not stack with the attack power from blessing of might, which means that physical classes can now be 'fully buffed' with a single paladin in the group.(gift of the wild also becomes the same buff as blessing of kings, so in theory no paladins are actually needed in a group anymore.
The other two buffs that are important are Windfury(which now also increases ranged attack speed) and Strength of Earth Buffs, both of which are available from various sources.
Good News: haven't verified it with an accurate timer yet but our global cooldown now seems to be 1 second. This increases the usefulness of haste significantly as the steady shot haste cap is now 1 second.
Rotation/shot priority:
Your rotation and shot priority will likely be somewhat as follows:
You'll engage the target with a serpent sting and pop kill command and chimera shot right away. It then becomes the task of watching your cooldowns and master marksman while you spam steady shot. In theory arcane shot could be used as a focus dump but then that reduces the number of steady shots (thus less haste gains from improved steady shot and less procs of master marksman).
Results:
Target Dummy with self buffs: 8.3K DPS maximum.
Raid buffed in Naxx10 (did 2 bosses) about 10K
These numbers are with having just learned a new rotation, and room for significant glyph and talent improvements and with many screw ups in the rotation. (and without speedy actions addon which appears to be broken now). This is with full 264 gear plus 277 bracers and Exalted Ring, and also without any addon support for helping to spot the "Fire!" buff.
So in conclusion I would have to say that with a little bit of relearning things Marksmanship's future as a strong raiding spec is still alive and well.