Well I don't use Outlook anymore and I'm strictly a Google Apps for email and my calendar kind of girl now.
What I have set up on my Google Calendar (which I use Google Sync for Blackberry to wirelessly sync my calendars). I have several calendars as well, simply because I'm visual and like to have the different colours for planning.
I have my personal calendar which has everything that I'm doing whether personal or business related. Then I have separate calendars for each client or project (that I can choose to share with a client or not). I use each of these calendars to set reminders, follow ups, and milestones for projects. I also have some calendars of my clients to monitor activities or events they have going on.
Each of these calendars sync with my blackerry, but only sync to my calendar on my blackberry, because as far as I'm aware you'd have to have a separate email for calendar to have them a different colour. This isn't a big issue for me since my Google Calendar is my default resource and I simply have everything on my Blackberry for reference when I'm out and need to confirm my availability.
Now to answer your question about Outlook and Blackberry, I would think your best bet is to sync your Outlook to Google (using Gsync I think that's what it's called) and then use the
Google Sync to sync your calendars to your Blackberry.
When you initially set up the Google Sync to your BB it will only set up your default calendar, but after it's done it's first sync simply choose options, scroll to where you see the calendar and then click on the calendars and it will give you the option to choose which calendars to sync.
Phew, that's the way I go at least. Give me a shout out if you have more questions.