iPhoto is one of the nastiest programs around... I've always found it clunky when the library gets large (even on 11 with a new system, the scrolling is not seamless)...
I hate the organization of files:
Year Folder >> Month Folder (12) >> Day Folder (~31) >> Picture
Who does this anymore? Even Camedia (the worst in the PC world) has abandoned this structure.
It makes Originals on any picture you even open (not necessarily edit).
When it imports from say your Pictures folder, it leaves your originals behind AND creates a copy inside the "no touching" iPhoto Library.
It does horrific things with thumbnail caches (I've seen thumbnail libraries get to 20GB without rhythm or reason).
And it has no proper duplication finder.
My vote for the simplest photo management with terrific tools is Picasa.
It's fast, automatically finds duplicates, leave's your pictures where you think they should be (Pictures folder), doesn't force you to adopt an archaic folder structure (you name the folders any way you like), has wonderful albums that allow you to pare down your photos in creative ways, and has built in web sharing (1 GB), and it allows you to revert any changes you make on an image (this uses a hidden Originals copy). And it's Free.
The downside: it doesn't integrate with iMovie, iTunes >> AppleTV.
--EDIT--
Clarification: your Picasa ALBUMS do not sync to AppleTV. Your folders can.
Apple TV can sync to your Mac's "Pictures" folder or iPhoto Library. So if you use Picasa all you have to do is point it to your "Pictures" folder. What ever is in your "Pictures" folder can be synced to Apple TV.
Also, migrating from a PC to a Mac with all albums intact is a bit of a challenge, but doable.