Here's the answer but not the fix.
WTF? I have 28 GB of the 30 GB available on my Touch and it only takes me about 30 seconds to back-up my Touch when I plug it in.
What's wrong with all your chit?
EDIT: I take that back. Now that I installed 3 "pages" worth of apps on my iPod Touch this most recent back-up is taking me 10-15 minutes. The one previous to this only took a minute. What gives?
I have the 16gb Touch. This is my 5th iPod. With each iPod, I've used, there have been some problems that Apple finally fixed with updates.
We know that it wouldn't make sense to back up your music, videos, podcasts, pictures, games, and programs as they are always on your PC in iTunes.
So what is being backed up?
Unique data!
The unique data the programs store, they create, they cache, you create, along with emails you downloaded to your device are being backed up and that's the problem along with the size of the data.
I bought my iPod Touch to replace my Palm T3 and use it as a PDA. Allot of the programs I downloaded are to help me get out of the office. Unfortunately, they generate allot of data baggage. My backups takes about 2.5 hours. I am willing to bet if I remove my emails, my downloaded pictures and the baggage programs, I could get quicker backups. What to look for to reduce data baggage is any program that downloads unique data from the internet and stores it on your device to use offline, i.e. RSS data, emails, databases, web saved pictures, ftp file storage to your device, etc.
Some of the "clairvoyant" programmers have added options to turn off backing up this unique data during the backup process. They should be written into my will!

Apple must be encrypting this data to your PC and that may need to be tweaked. A better transfer protocol might help as well. Right now an option to turn off this unique data backup would be Apple's best "quick fix" solution.

Things to help

:
- Clear your old emails.
- Clear your Safari cache.
- Only carry those ftp transferred files you really need.
- Set NYTimes to only save 1 days worth of news.

- Limit the amount of items stored in Pocketpedia.

- After downloading your web pictures or pictures from your camera to your PC/Mac, delete them from your device and let iTunes manage them.
These are only a few suggestions to try instead of canceling your backup for the unique data you really need backed up. Remember, if it's in iTunes it doesn't need to be backed up during the backup process. If you have a few tips, please share.

My last backup stats

:
Time - Fell asleep waiting.

Number of files - 6,193
Smallest file size - 117b
Largest file size - 174.4mb
Total size - 1,197,439,579 bytes = 1.2gb
I found this information on my Windows PC in "C:\Documents and Settings\Owner\Application Data\Apple Computer\MobileSync\Backup\". On a Mac, someone will need to look this up. As you can also see, these backup can take allot of hard drive space.
If this helps you, reply back to this post and let me know.
Daniel