I agree completely with marc11. Excellent advice, especially in terms of the TONS of stuff you can do with the Macbook Pro, vs the ATV 2 that is really pretty limited, in the sense that it is there to purchase iTunes movies and music, stream your iTunes content using home sharing, and a few good services notably Netflix which has great integration. That said....
Pros/cons, like in other contexts, depends a good deal on what you'd like to do:
Macbook Pro pros:
1) If browsing is a priority, Amazon Prime, Hulu, other video sites, content, etc.
2) You can play whatever you want!
Macbook Pro cons:
1) Netflix remote control ain't there! (what can I say - I'm a couch potato!
2) Can be somewhat complex to set-up regarding mirroring, etc. (I admit, this one really just depends on your level of ease with A/V stuff)
3) I don't know - do you have a safe and reasonably good place to stick the laptop near the tv? Or are you going run some wires?
ATV 2 pros
1) IF all your content is already in iTunes, then it is easily accessible with a great UI in Home Sharing
2) You don't want to browse or go to other sites, and you're psyched for your iTunes rentals and content.
3) You're a big Netflix fan who likes using a remote control (!!)
4) Utter simplicity of use
ATV 2 cons (assuming it's not jailbroken...
)
1) If it isn't iTunes compatible video/music, you can't watch it!
2) If you like watching movies on ANY channel not officially supported by Apple, you can't watch it!
3) Your content can't be accessed off a hard drive, etc. (again assuming you're not jailbreaking)
ATV 2 seems to me to center around three big things (though certainly there are other features than these three big ones) and that's it: Netflix, iTunes rentals, and Home Sharing. It is the quintessential Apple product, to my mind. That is to say, it only does a few things and these are locked down pretty well by Apple. However, it does those things extremely well. Everything is smooth and works just as advertised. So if you've got $99 and really just want to stream your iTunes content and watch Netflix, I think the ATV 2 is frankly worth every penny.
On the other hand, if I'm making too big a deal of the Netflix remote control and personal content that isn't compatible with the ATV 2 doesn't matter, then by all means just use your Macbook Pro. That is a great computer and it will do everything you need! My final word being, again, Pros and Cons are only those things depending on what you need!
Good luck! And I'm saving this for last: I'm assuming you have a relatively recent Macbook Pro? It doesn't necessarily have to be, but hopefully your computer is fairly up-to-date. For example, I have an 15" 2.5 Ghz/6Gb/1TB 2008 non-unibody Macbook Pro and it would be great, but there's no mini Display port, so I would have to use a DVI-HDMI adapter and add an 1/8" audio cable...kind of a pain.
