Mirrorless may be smaller than DSLR but you have to consider is it smaller enough to make the difference? While I still have the E-P1, I don't use it now as it isn't smaller enough over a DSLR for "carry everywhere" and I've reverted back to a high end compact in that area.
Of course the more modern m4/3 bodies are a fair bit smaller now, and Panasonic's X series standard zoom is also small too so that could be a potent travel package, possibly with an extra lens or two for more options when you can carry more.
And obviously, whatever you buy, you better get it sooner than later so you can get used to using it before you go away.
_________________Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.