What is your reason for asking?
If it is just because you're hoping to get an iPad 3, then as the others said... probably next spring. If you don't mind waiting that long fine... otherwise jump in now.
IMO, an upgrade is an upgrade. The iPad 3 will be better... but will it likely be something you need? My guess would be better cameras and higher rez screen (maybe), along with a boost of processor and memory.
Better cameras would be nice, but unnecessary depending on what you intend to do with it. The cameras in the iPad 2 are fine for video conferencing, maybe taking some video and editing... not much else.
Higher rez screen... maybe my eyesight is just lousy or something, but I don't really get this one. It seems to be a popular thing wanted though. I can see the advantage of a higher dpi on a small device like an iPhone if you have good eyes, but I don't see the need on an iPad where you have screen space and generally hold it further away. We've had a similar dpi on our home computer and laptop displays for years now, and that dpi seems fine to me.
Processor and memory boost... the iPad 2 seems pretty snappy to me with anything I've done with it (and, I'm trying to replace my laptop with it... so I'm doing more things than a hobby user). More performance (so long as there isn't a battery life trade-off) is always welcome though... but needed? More RAM would be great, but again, the iPad 2 seems to have enough to have gotten over the hump where it was really slowing things down.
I'm guessing that I won't be upgrading to the iPad 3 unless there is some big surprise feature that I need/want. As others said, I don't think it will be like the iPad1 -> iPad 2, where it really made an incredible usability difference. The one thing that *might* get me would be a rear camera upgrade with enough rez and light gathering ability to be able to use for scanning pages at a library for research (something I have a specific use for and is currently lacking in the iPad 2).