Oh my gosh, you are so funny! my fiance' and his mother and I had a HUGE "discussion" about this very thing!!! It is the only major issue we have had so far! I really wanted to do a simple postcard, and they really wanted a full invite.
At 7 months out, we ended up sending a greeting card style invite. It had a pic of us on the front cover from when we got engaged in Cabo, with the sunset behind us. When you opened it up, it had a brief informal invite that referred people to our website. I can send you the template if you want. Our guests LOVED it!! Everyone has it on their fridge. And then the people who aren't coming can still post something to your guestbook or find out where your registry is. The only problem is that a bunch of people we didn't expect surprised us and decided to come. Good luck!