Fishmed,
Hmmm... I never actually tried it, but I presume that the Acid loops are useable elsewhere. I think they are just WAV files with some tempo mapping stuff that ACID uses stored in the file header (they call this "acidizing" the file), and other applications would ignore... but I'm not sure.
As far as the advantages of using ACID Pro rather than Cakewalk to construct loop-based music -- well, there's no comparison. It's almost like building furniture with a small set of fundamental general tools -- hammer, saw, drill, file -- as compared to having a shop like Norm's on "New Yankee Workshop." Linking and layering loops in Cakewalk can certainly done but it's tedious trying to get tempos to match between one loop that was recorded at 110 BPM and another at 120 BPM... In ACID, all the tedious and hard stuff is done automatically, and you can get a set of loops working smoothly together in no time.
Of course, ACID Pro costs a fair bit of money, but considering it comes bundled with Sound Forge XP 4.5 and one of the Sound Forge FX plug-in sets (FX1, I think) makes it a better deal... then there's the "lite" version, ACID Music, which might do all you need, and is less than $75, I believe.
-AlChuck