How to backup with Time Machine for complete clean reinstall of OS

Question

My iMac has been getting slower and slower as the months go by and with each new software update. It used to be a lot faster than this when it was new.
I'm thinking the best solution might be to do a complete clean reinstall of the OS. My question is, if I have Time Machine backing up of all the users Documents, Email, Address, Book, iTunes Library, and iPhoto Library files, can I just go ahead and blow away everything on the machine? That is, after reinstallation, can I just plug in the hard drive, turn on Time Machine and get all those data files back in the right place without difficulty?
Or am I better off meticulously and manually moving the appropriate files/directories to an external harddrive and then fitting them all back into place manually afterwards?
(NOTE: I used to have to do a clean re-installation of XP every year or so to keep the system nice and snappy -- it would invariably get slower and slower over time. Since I got my iMac (Tiger) I had never had this creeping slowness problem, why is it happening now with Leopard?)

Answer 1

slegge,
This might give you some ideas.
Using Time Machine to Restore You Entire System
Q: Can I restore my Mac from a Time Machine backup?
A: Yes, you have several options: (In all cases Mac OS 10.5 Leopard is required as previous OS X versions will not work with Time Machine backups.)
*Full Restore Via Migration Assistant & Time Machine*
You can use the installation DVDs that came with your Mac and reinstall Leopard (Mac OS 10.5). During the installation process you will be asked if you would like to Migrate data over from your Time Machine backups. The advantage here is that you start with fresh system software. The disadvantage is that you may lose many of the personal preferences/settings that had been established with the previous system. But this may be only a minor inconvenience to reestablish these. Depending on whether you choose to migrate your applications over as well, you may be required to reinstall any 3rd-party software or standalone Apple programs. Don’t forget to run Software Update once the initial installation is complete to bring your system up to date. Using Disk Utility at this point to repair any permissions issues is advised as well.
*Full Restore Via Time Machine Only*
Alternatively, you can use the installation DVDs to do a full system restore. Insert the installation DVD. When the welcome window appears, go to the Utilities menu and select “Restore System From Backup…” and choose the drive that your Time Machine backups are on. Then select the date of the backup you would like to restore from. This will completely erase your internal drive and restore your system to a relatively same condition it was in on the date of the backup you choose. (See this article for a list of files that TM does not restore, http://shiftedbits.org/2007/10/31/time-machine-exclusions/) The advantage here is that you retain many of the personal preferences/settings that had been established with the previous system. Additionally, no further installation of 3rd-party software is required. The disadvantage is that BECAUSE you retain many of the personal preferences, settings, and system files that had been present with the previous system, you run the risk of reintroducing problems you experienced with the previous installation, including any issues that necessitated the OS reinstall in the first place. Using Disk Utility at this point to repair any permissions issues is advised as well.
*Full Backup After Restore*
Bear in mind that in all cases Time Machine will perform a full backup after a full restore. This is normal. Time Machine will resume incremental backups after the full backup has completed. To view previous backups, Control-click or right-click the Time Machine icon in your Dock or Option-click the Time Machine menu extra and Choose "Browse Other Time Machine Disks," then select your previous backup volume. You will enter Time Machine and be able to browse your previous back ups and restore files. (http://support.apple.com/kb/TS1338)
Hope this helps.
Cheers!