IPB 3.2 is coming out sometime this year. No release date set but it'll probably be somewhere around 6 months, but in 2011 for sure.
No point to switch to IPB 3.1 just to go through all the hassle of going to 3.2. But yeah, you should move over to ipb.

Just looking at the general comments, the majority of people who voted VB did so because they are familiar with it in the warez scene (It was the best for it's time). Looking at the people who support IPB, the majority of us are ex-vb users who switched and now like it better for tons of reasons.

My final word, wait for IPB 3.2 and switch directly to that. Sorry to say this, but it is a better platform then vbulletin and the new community is growing by the day.

ps. I switched my medium sized forum from vb 3.8 to ipb 3.1 with no real problems. Some small stuff was lost, but anything important was kept.