The three most probable causes of a slow booting computer are a failing hard drive, a malware infection or too many startup items.
Since you say it's betting getting slower over the course of three months I suspect the drive is failing. Regardless if it is that or not you should play it safe and immediately backup all your data, bookmarks, adress book, etc.
There is a possibility that it's malware or startup items but backup that data first.
What antivirus and antispyware programs do you have.
What are the items that are loading in the taskbar that you keep deleting? When you say taskbar I assume you mean the notification area or system tray at the right of the taskbar.