Yep, I've watched all the developers Let's Play (check their youtube channel), and it looks like it is going to be awesome.
Also, not too much like minecraft.

From the FAQ:

We should probably set up an Allegro server when the game comes out

looks great, the principe is great but minecraft causes eye cancer so this is a good alternative

I've been watching the developer and tester 'Lets Play' videos and right now, there are more craftable objects to make than in Minecraft. I don't think there will be the equivalent of redstone circuitry though.

The worlds in Terraria are definitely not 'infinite' like in Minecraft.

Which is why they are not too much alike.
Terraria is focused around exploration, crafting and fighting enemies, whereas Minecraft is about building cool megastructures and cute little project.
Just because games share a few mechanics (in this case destructible\constructable environments and crafting) does not mean that the games are very similar. Just see what the developers playing Terraria spend most of their time on in the LPs (exploration and fighting) and compare that to what you spend most of your time on in Minecraft (Digging for iron and building cool stuff).
And just because I like crappy analogies:
Red Faction: 3D real time action game with destructible terrain.
Liero: 2D real time action game with destructible terrain and grappling hooks.

The trailer makes it look nothing like Minecraft because it looks like an action game, whereas Minecraft is not an action game.
I'd say they are less similar than AudioSurf and Those rhythm based shmups that began surfacing a while ago.

But this is really too long a post for such small a subject, so I'll stop here and resume anxiously waiting for Terraria.

I heard the water mechanics for this game were much more in-depth. Supposed to have water pressure and pipes and such...

I would argue that the differences are natural, however. In 2D, it's much more difficult to build interesting things in-game. In 3D, you can create pretty much anything with enough "pixels" AKA blocks. So traditionally Minecraft players have focused on the creativity side because the combat and [non-existent] story elements haven't really matured yet (probably because 3D adds a lot of complexity to everything). In Terraria I think it would have been an epic failure if they took that approach with development. Instead, it looks to me like they started out with a Minecraft base, translated to 2D, and built a 2D gaming experience on top of that. Not only is it fair to compare to Minecraft, but I think it's fair to call it a ripoff, albeit one that inevitably moved in a completely different direction (though I don't think I saw anything particularly original).

To me, Terraria looks like what expeienced 2D gamers (with programming and graphic experience) would come up with if they attempted to duplicate Minecraft in 2D, simply because a lot of things that Minecraft achieves are much more difficult (or impossible) to mimick in 2D, requiring you to change things around. The grappling hook, for example, looks to me like a necessary deviation. I would imagine that they started out with Minecraft in mind and the project naturally deviated. I think it's great, but I don't think it would be fair to say that Terraria wasn't greatly influenced by Minecraft.

Fuck, lost a whole post... lets try this again...

Yeah, so I saw the video above, and sent it to my office mate who I play Minecraft a bit with, and he goes, "yeah that's the game I was talking about!" He had just got done reading an article on Gamasutra on Cellular Automation... I haven't read the article yet, but from the first couple of paragraphs, I think he may have been confusing the titles of the games...

Just having watched the video above I can see that... It also made me realize, Notch (possibly unknowingly) is definitely lying when he says he just wants to make Minecraft fun... He's pushing a couple of different things, and fun is not at the top of the list... mostly he's pushing for theme, and I think also difficulty... he pushes the theme a bit here and there, but not by much -- just look at this video these guys are like "laser guns? those are fun, throw them in. who cares if they don't fit." This game is going to rock.