Studio Pro is a much more comprehensive program, with way more options than iDVD, including fully customized menus, subtitles, preparation of a project for commercial replication, and as Jerry mentioned greater control over the encoding – but of course you have to buy the full Final Cut Studio to get it, as it’s not sold separately any more.
If you are serious about video editing and have the budget, then getting Final Cut Pro Studio is worthwhile, and investing the time in learning DVD Studio Pro.
But as a freebie iDVD isn’t bad at all, and will suffice for basic use. These days a lot of video ends up online in HD and DVD distribution is the “country cousin” quality-wise, so DVD SP is less of a key program than it was.
Now if Apple would only support Blu-Ray authoring in DVD Studio Pro…
