I've been using Macs for nearly 20 years. I've made hundreds of DVD's using iMovie and iDVD. They are very nice programs, but they have serious problems.
You can work around the problems, but I pity the unsuspecting beginner trying to get good results with this software. Many of them throw their arms up in the air and give up (their comments can be read on the Apple forums--before the admins delete their posts). They're the lucky ones. Others succeed in making DVD's but discover later on that their trust in Apple software caused them to lose time, money, and precious videos. I've been there!
The most serious problems are:
1. Quality. Several books on iMovie and iDVD have been published. The authors claim that there is no noticeable loss in quality when encoding up to 90 minutes in iDVD 3 or when using Best Performance in later versions. This is nonsense. If there is any fast motion, the quality is terrible. This problem is easily resolved. Use iDVD 4.0 or later and use Best Quality for anything over an hour. If there is fast motion, try not to go much over 90 minutes per DVD.
2. Synch problems. After you finish editing in iMovie, you should select all of the clips on the timeline and extract audio. Otherwise, you are likely to get synch problems. Although user errors can cause synch problems, there is definitely a software bug that also causes it, and it should have been fixed by now. This step takes valuable time and disk space. It takes about 15 minutes to extract the audio from an 80 minute video. This is very annoying when you are trying to get work done.
3. Non-playing DVD's. I first noticed this problem with iDVD 4.0.1, but I recently had it happen with 4.0. You burn a DVD that will play in your computer but not in a DVD player. Many people were up in arms about this and other problems on one of the Apple forums. Their posts were deleted. Apple apparently wants to hush this and other problems with iLife 5. Fortunately, there is a work-around, but it took a couple of weeks to figure it out (during which my DVD projects had to sit in limbo). Go into System Preferences and set up a user that is only permitted to run iDVD. Then burn your DVD's using this account.