I figured I would give my experience within the categories. I am currently a cat3, and could have my upgrade to 2 next season if I tried. In Montana, we race the 3's with the pro/1/2's due to field size. I have also raced cat3 only races as well, so that's where my upper category insight comes from.
Category (cat5) - The races are anywhere from 35-60 miles long. Usually you will race with the cat4's. Expect some fast guys trying to eek their way through to the upper categories... They will usually be the ones NOT pulling, but near the front. The guy that gets bored and takes massive pulls at the front will usually be dropped in the wind up for the sprint. If there are climbs in your race, there will be attacks on the first few ups, so be ready and near the front. If a break away succeeds, it's usually because it got away on a longer hill. As a cat5, try everything! Sit and watch, go take some pulls, shake things up with an attack or two. Get as much experience as you can in the 10 races you need to do before you upgrade to cat4.
Cat4 - Usually the same as the cat5's, but you know who's who and who/what to watch for. Try to be near the front. It keeps you somewhat crash free, and it's less work than the constant yo-yoing in the middle or back of the pack. Leave the attacking to somebody else! The only thing you need to do is make sure nobody of importance gets away. If you're in the front all of the time, you're not dropped. If you find yourself still in the top 10 in the last Km of the race, congrats! Now comes the fun. Someone is bound to get antsy and throw down a little past the Km sign. Depending on your strengths, that's your boy. Be 4 riders back from that guy. He'll realize the error of his ways, and probably slow down at the 600m, and that usually makes someone else go for it. Get on them, and wait for the 200m sign... It's up to you from there.
Cat3 - The races become longer - usually 60-90+ miles. Things can get strange from here on. Teams come into play, and tactics become important. Find a team and start training with them as you learn the game. Your first few races might see you working your ass off to get somebody else across the line, so don't expect much in the win category. If you don't have a team, don't waste your energy. Sit in and get near the front (recurring theme). Make yourself invisible until it counts! Riders are finding their strengths and they know how to make people hurt, and same goes for you. If you find yourself in a break and you're a climber, you have it easier. Wait for a hill, get on the front, and rain the pain. Climbing is slower (duh) so drafting becomes almost non-existent. If you hurt, they hurt. When the hill crests, let the other guys take over and save yourself for the finish.
Cat1/2/pro - These categories are fast on a whole new level - A level that can leave you scratching your head as the rest of the group rides into the distance. You're racing with pros. Think about that before you do anything stupid... But by now, you should have a team and know your responsibilities. If you feel like you can't do your job for a certain race, SAY SOMETHING, as your teammates are counting on you to do a job. Not doing that job can ruin the race for the team, and possibly send you looking for a new kit.
If anyone can add or subtract anything, I welcome it.
Sticky this maybe?