I use my iPad constantly. I got it on April 3rd. I got an iPhone 4 this month. Would I have felt bad if I picked up an iPhone 3GS just before iPhone 4 came out? Yes I would. Would I feel bad about buying an iPad now versus waiting for next year? I don't know because I don't know the features just yet. But Apple isn't known for piddling around with upgrades. They tend to make meaningful, tangible upgrades for each product cycle. Knowing this, I would consider whether you need the iPad form factor now. For me, the biggest deal is not the capability of the iPad, especially in light of all the limitations of iOS 3.2, it is the form factor that I need. Consider the usage you would get. Six months of being able to web surf on the couch or in bed and the ability to sell it and get the new model if you feel you just have to have face time or retina display or whatever the new model comes out with.
To me the lowest risk is to buy one now and enjoy it for 6 months because Apple gear tends to retain value. History suggests you will be able to get a decent amount for a used 6 month old first gen iPad even after the new one comes out and you won't be stuck 6 months using archaic form factor devices because you held off buying.
Macrumors offers a "Buyer's Guide" and even when the status changes to "Don't buy, Updates Soon" the bottom line is if you need something you simply buy it when you need it. The buyer's guides is more intended to help people who might pick something up on impulse only to find a much better model comes out 31 days later.