Hold on here! A slow booting system needs some TLC.
But, before you go down this path make sure you have a good backup!
To start with you likely need to check your HD's permissions & disk. To do this effectively you'll need a bootable external drive (OS-X) or if you have a newer system with a recovery partition you can boot up under it. Run Disk Utility you may need to run it a few times to fix all of the errors.
The next step is to clean out some of your junk, You should have about 1/4 to 1/3 of the drive free. You may find using this tool from the App Store will make the job easier: Disk Doctor. So after cleaning things up the last step is to defrag your hard drive. Here is the tool I use: Drive Genius. In both cases there are other Apps out there that will do the job.
The last step is letting the system run for awhile. Behind the scenes the OS is doing some magic! It needs to index all of your files and organize things. In the end your system should boot up as fast if not a little faster than Mavericks.