More Than a Feeling - G C Em D
Holy Grail - E A C#m B
The pattern of the chords is the same, in a different key, and there's a couple extra palm muting on the minor chord in the Boston song (Holy Grail only mutes between chords) and a kind of passing C chord from the D back down to the G that Holy Grail seems to ignore for the majority of the song. Nitpicking things of course, but at best it seems like some kind of homage rather than a ripoff. Certainly gets a lot of attention though.
Now, compare Holy Grail to Nikki Webster's 'Strawberry Kisses'. I'm surprised not many people look at this one (well, besides the fact it's beyond crap) because the chords are exactly the same, same key and progression. Either it's stolen or it's just a common chord progression. The Troggs' 'Wild Thing' does something similar but uses a major chord instead of a minor.
I could be wrong of course but that's just how I see things this morning.