When I bought the Pod XT Live, I was delighted to find that it came with the FX Junkie pack installed. Next addition was the Collector Classics, which has some great sounds in it. I'm not a Metal player most of the time, but I like to cut loose once in a while

, so when I had the cash I bought the Metal Shop pack to complete the collection that was available at the time. Later, the Bass Expansion came out, but I only added it recently as I've been getting into playing bass. I've also collected some favorite tone presets that take advantage of all the Model Packs. I feel like I have everything I need for any situation calling for a certain guitar or bass tone.
I agree, the model packs really open up your capabilities for getting some sweet tones. On the other hand, I know folks that say "This thing already has more tones than I need!" and are happy with the stock unit. Take advantage of the Model Pack deals, you won't regret it!
BTW, if anyone's interested, back when I had more free time I created a couple documents listing the amps and effects available with a fully loaded Pod XT. THey are PDFs that you can print out, tape together and hang on the wall of your music room- collect the whole set!:D
Hopefully these links will work:
http://www.vettaville.net/PODxt3-Amp-Sheet.pdfhttp://www.vettaville.net/PODxt3-FX-Sheet.pdfYou can see them hanging up here:

Enjoy!