Seriously do consider the 30" ACD, I got it 3 weeks ago, and it blows my mind. I use it with Adobe Suite, FCE, Aperture etc, the screen real estate is perfect. Plus it is one of the most beautiful things I have ever bought, it looks beautiful.
I'd personally just get whatever looks better to your eyes. Both screens have the same resolution...if you prefer glossy go with the ACD, if not, go with the Dell.
I have the LED Cinema Display that you are talking about and it is a great monitor. Keep in mind though that it will ONLY work with computers which have a mini-DisplayPort connector. That means you need the latest Apple hardware, whether that is an aluminium MacBook/Air/Pro or the latest revisions of their desktops. Previous generations of the hardware are incompatible and there are no adapters available whatsoever.
It's for this reason that I'd advise against buying it. I got mine at a big student discount and it was miles cheaper than the Dell, but I'm sort of regretting it now. I'm worried that in future I will only be able to connect it to Apple branded hardware because no other PC manufacturers or graphics card makers have shown an interest in producing compatible parts.
You're gonna get a huge mix of opinions on this topic, but oh well.
As for me, I use a Dell 2709W, and I love it. Since my eyes aren't the greatest, the higher dot pitch compared to a 24" of the same resolution helps a lot actually. That and the huge amount of inputs on the back allow it to be my all in one solution for my PS3 and Wii.
I'm actually also planning on getting a second one, as soon as I have extra cash to spend and when Dell has another half off sale