Good points, Justin,
And, per the FAQs to the right of this forum, the easiest way to find out what's up with your DVD burns is to break the process down to individual steps.
Even selecting the option to burn to a folder on your hard drive rather than directly to a disc can tell you a lot about where your transcoding is bottlenecking -- or if the problem is as simple as the program not interfacing with your DVD burner.
What happens when a Project is Burned to Folder, or to Disc is that first the entire Project is Transcoded to MPEG-2. This is done via 2-Pass Transcoding to get the highest quality, in the smallest space. During this process, PrE looks closely at the footage on the first pass, and then makes notes to itself. It then uses those notes as it makes the second pass. During this, there are basically two files created: the Video and the Audio in elemental streams. This is what is usually shown roughly in the progress bar. Next, those elemental streams are then muxed into one MPEG-2 file. Starting here, the progress bar usually sits statically. Next the Sonic Authorware module, Vobulator, takes over and gathers up the Menus, and looks at the navigation. The number of Chapters will determine how many Scene Selection Menus are needed, so there are some calculations going on. Next, the Vobulator takes all the Menus, plus the MPEG-2 file, and packages them into the commonly seen VOB containers. It is not until this time that PrE really knows how large the file is going to be. After the second pass, it has an idea, but until everything is into its proper container, it can only guess. Now, the structure of a DVD-Video, the VIDEO_TS folder is created, and the VOB's are written to that, along with the IFO, and BUP files. Then, the working files are all cleaned up. This is all going on with the progress bar not really doing anything. If there is a physical Burn to Disc, then the progress bar will probably change over to Burning, and will once more become active. Unless one has very slow blank media, or a very slow burner, this usually takes much less time, than the Transcoding and Vobulator work.
There's a lot that goes into the process. Also, until Transcoding has completed, and the Vobulator starts reporting on the navigational Assets, PrE can only guess about the space required, based on the Duration of the Project. When it has gotten well into the Project, it then finds the total space required.