These are good points. A redesign, if it comes, generally entails a less reliable machine to at least some degree. Think about how long the current cases have been around and how fine tuned they are now. I am buying now for that reason - I bought my PB G4 when it was one of the last revisions, and its been rock solid, and I'm doing the same with this MBP. Plus, when you look at performance, there is no strong reason to wait for Montevina. Montevina is a chipset, not a CPU (PENRYN will continue to be the CPU) and will provide at best fairly minor performance increases over the current chipset (Santa Rosa). If you were talking about waiting for NEHELEM, the next Intel CPU, you'd have an argument, but you aren't. Toss in the fact that Apple may not even update in June (they may wait until later in the year), and if they do update, they may not redesign (redesign could be held off for Nehelem), and the reasons to wait decrease.
In closing - if you want an iPod and can afford to wait until June that makes sense, but otherwise, I don't see too much disadvantage to pulling the trigger now.