Ok, so I've been trying to learn some theory, and i've read the Crusades and some other articles here on UG. Now, I've looked into some chord progressions, and I was wondering what the difference was between, say, a G7 and Gmaj7?

Then say I was in the key of C and i was writing a chord progression I-IV7-V7-I, would I want say a Fmaj7 and a Gmaj7 or a F7 and G7?
yes to the first.. and yes to the second
The only difference is dominant7 has a flat seven
the V7 is the only dominant chord in a major key
so G7 is G dominant 7th while Gmaj7 is a Gmajor chord with a 7th?

Well, what one does the IV7-V7 imply?
G7 chord tones- G (root), B(major 3rd), D (5th), F (the FLAT 7th, doesnt matter if chord is minor or major, this is flat7th, or a whole step below the root)

Gmaj7 chord tones- same, but F# rather than F, which is the natural, or major, 7th

if its IV7 then its F7, if its IVmaj7 then its Fmaj7. but you can make a decision too, which one sounds better to you
dont take any guff from these bastards man

Quote by Fenderhippie69
I only smoke when I've been drinking and I only drink when I've been smoking.
Well, the diatonic 7ths of C major are fmaj7 and g7, so those would stick closest to the actual key. F7 wants to resolve to Bb more than C, so I wouldn't use that.
Well if want to stay strictly in the key of C it would be Fmaj7, which contains the notes F A C E and G7 which contain G B D F. all those notes are in the key of C!
Quote by Stolen Identity
so G7 is G dominant 7th while Gmaj7 is a Gmajor chord with a 7th?

Well, what one does the IV7-V7 imply?

G dom 7 is a G Major triad with a minor seventh

Gmaj7 is a G Major triad with a MAJOR seventh

Get it? They are both built off a major triad, but have completely different functions.