You'll hear this from a number of people, but I'll be the first it looks...
If you need now, then get it. No sense in waiting. Otherwise, if you can wait, then hold off until June gets a little closer, and more information comes out.
Remember though. With a new OS and potentially new hardware, there'll be huge delays, and possible bugs. When the 3G came out, people had all kinds of issues activating, etc. plus limited quantities. If that's okay with you, then wait.
I love my 3G. I have no regrets at all. Same with my MB. I bought it about 6 months before the new Alu.'s came out. I'd love one, but I'm happy with the one I'm using right now. I've been productive for 6 months, and couldn't be happier...point? Don't play the "Wait until the newest/best/greatest one comes out" syndrome.