I usually catch the 6:58 or 7:12 train, and there is plenty of parking available. I also sometimes take the 7:42 train, and while you might have to walk a little further, there is still parking available. Parking is $1.25 per day as of 7/1/08. Metra is currently updating the lot and platform, so some of the parking spots are taken up by construction vehicles. The parking congestion should be better once the upgrades are done.
Depending on where in Cary you live, I've heard that some people use either the Fox River Grove or Pingree Station lots due to the parking issue, but I've never had an issue with finding a parking space.
The train ride from Cary to Ogilvie (downtown Chicago) is a little over an hour if you catch one of the express trains, but can be as long as 1:20 if you catch one of the local trains (stops at all stations). Check the schedules at http://www.metrarail.com.
The beauty of living so far out is that since it is one of the first stops, you always get a good seat. When I was riding the train from Palatine or Arlington Heights, there were often times when it was standing room only. One hour on the train sitting down and reading a book is better than 30 minutes standing crammed in the vestibule with a half-dozen other people, in my opinion.
We relocated to Cary in July, and so far we love it here. It is a quaint, quiet community. We liked the fact that it had more of a small-town feel than some of the other suburbs that seem like endless strip malls, big-box stores, condos and apartment buildings.