Raider,

Yes it's worth it - but it's not a huge improvement. Not subtle either. Somewhere in between.

Any program material that sounds good in 5.1 should translate well to 7.1. And of course DD EX and DTS ES source material will show it off the best.

Since you only need to add two speakers to make a go of it, if you have some old "cheap" ones kicking around you could try them first. A pair of old RS Minimum 7's for example. (Don't we all have a pair or two of them tucked away somewhere?) If you then like the effect, jump in with something to match your other surrounds (or compliment them - whichever works best for you. ie. I won't get into the whole di vs bi vs mono-pole discussion.)

Have fun.

Jeff Mackwood