I'm in the same position and am waiting on the Olympus. To answer your question of which phone to get, that's entirely up to you.
For me, I'm in a peculiar situation. I HATE my BB so want an upgrade as soon as possible; unfortunately, the miserable GPS on the Captivate forced me to not get it (I use GPS constantly). That made me wait for the Olympus. The issue with the Olympus is that it's impossible to root it, which is something that I like doing. So my choices are either to get the Olympus or wait even longer. Since I hate my BB, I'm not going to wait any longer...
If you're worried about updates (and don't mind the lack of GPS issues that the Captivate has), then I'd suggest getting the Captivate and rooting it. You can get updates MUCH faster than when AT&T releases them (ex.: Froyo never came and will not be released on the Captivate "officially"). Also, with custom ROMS out there you can probably approach speeds to what the newer phones will be able to reach (CyanogenMod can make Droid 1 reach Droid X speeds, for example).
I'm going to miss not being able to root my Olympus, but IMO I think it will be worth it. I'm sure there will still be plenty of stuff to do on it. And since the Olympus will be Motorola's "best" phone, I'm sure the updates will come eventually.
Just my 10 cents.