Did Coldplay totally rip off Radiohead?  

I wouldn't call them a "rip off." There are many many bands that are similiar to eachother but I wouldn't say that they're ripping anyone off, just that they've been highly influenced or their choice in sounds and songs is very similiar to someone else's. And personally, I like both groups :)

I've often thought about how similar both bands are but, I doubt that ColdPlay has ripped off Radiohead, at least intentionally. I think they sound alike because both bands probably have the same musical influences. So, if one's ripping off the other, I hope they continue because I like them both, a lot, and want them to continue making the kind of music they are. :)

Have you heard Thom Yorke's solo album "The Eraser"? I've heard some of the tracks from it and like it a lot. My favorite song that I've heard from the album is "Black Swan." You should check it out, if you haven't. It's very RadioHeadish.