I really love iChat. I think it's a billion times better than Adium in my opinion. Bonjour alone is really fantastic. Plus, iChat is super gorgeous and Adium is definitely not.
Anyway, there are a few preferences that I really recommend turning on to make iChat way better. To see your iChat preference, choose "iChat" from the menu bar, then "Preferences". Everything I'm going to cover is in the "Messages" tab, but there are definitely a lot of other fun things to tweak if that's your thing.
First, Save chat transcripts. Enable this preference to save all of your chat transcripts (duh). This is great (especially if you're using AIM since there is no way to get your logs online anywhere). I recommend choosing a folder in your Dropbox if you have multiple computers so you can see history in multiple places.
The next preference is my favorite: In new chat windows, show the last 25 messages. This is really great. You can close chats when you're done with them and not worry about forgetting what someone was saying. I constantly get people asking me to send them something again or are confused because they don't remember the context of our conversation. I highly recommend this one.
Finally, Collect chats in a single window. This may already be on, but if it's not, definitely turn it on. Now, instead of having a ton of chat windows, you get a really nice looks chat window that has a list of people you're talking to with their picture. It's really fantastic.
Anyway, hopefully that helps you make your chatting more enjoyable. Enjoy!
By the way, Verbs is hands down the most fantastic chat client for iPhone and iPad. Highly recommend.