IGN has a friendly debate between the PC and 360 guys about what version of Elder Scrolls IV: Oblivion is right for you:

Dan: Yeah... the PC version of the game is definitely going to need a burly machine to play well on high detail at high resolutions. What I played at the event ran pretty well with only a couple of hiccups in performance when there were a lot of characters on screen, but even then it wasn't unplayable by any means. That said, Bethesda told me that the specs of the machine I was playing on and it was a 3.2 GHz processor with 2.0 GB of RAM and an X1900 video card. That's a nice machine and it's all we've had the chance to play the game on. Who knows how the game will look or run on a machine with the minimum requirements? It's just something we're going to have to wait and see I guess.

But like you said, when it comes to performance, what we saw of both versions was strikingly similar. Load times were very quick (on PC to the point that I barely even noticed them and probably wouldn't have if it wasn't for the draw distance pop in) and frame rate was absolutely decent. Visually it's only a smidgeon better on PC if you look really hard like you said in the preview. Yeah, the PC has sliders for graphics capabilities, but that's not going to matter to high end users to which the 360 is most comparable. The only thing that'll make a difference to hardcore PC fans is that resolutions can be raised up to a level the Xbox 360 can't display.

For many people I think it's really going to be a matter of cost. If they already have the Xbox 360 and HDTV without the luxury of a great PC and monitor, I'd say that's an easy choice. For those with a great PC that don't have the console love, the choice is opposite, but equal in simplicity. The tricky part is when you get into the mix with those that have a lower end PC and don't have an HDTV or console. If their PC specs are low and they were thinking about upgrading it in any case, it's a good time to do it. If they like TV and movies a whole lot and don't care as much about PC gaming, it's probably worth investing in the HDTV and 360.

Honestly, it doesn't make much of a difference either way for this reason. High end PC users and Xbox 360 users will be so comparable that it's almost a matter of if you want to sit in front of the computer in a desk chair or on the couch. My inclination for a game this long is towards my comfy couch but that means I'll have to compete for the TV with my wife so I may yet play through the game on my computer.