There's a couple of schools of thought on bike cleaning. There's the damp-cloth-wipedown brigade and the 'hose it off' school. I suspect the former is typical of most roadies and the latter of mountain bikers. In this case - a medium dirty bike - 60 seconds with a pressure washer saved me a lot of work.
Whether you're using a garden hose or a pressure washer like the one I used at a commercial car wash it's ok - and often far better - to spray your bike clean when it's caked with mud. There's just a couple of things you'll want to keep in mind.
Firstly, make sure you remove anything that doesn't like getting wet. Erring on the side of caution, this would include most cheap lights and certainly any electronic gear like Garmins or other GPS devices and the like, which will do just fine in a rain shower but might not fare too well if they cop a high pressure blast. If you have a Brooks or other leather saddle, or leather handlebar tape, you will want to make sure that they're covered or otherwise spared. (I have no experience with electronic shifting ensembles, so ask your local bike shop.)
The other tip is that high-pressure water doesn't do the grease in bearings any favours, so don't go directing the spray at hubs or bottom brackets. (If there's a choice, skip the soapier settings.) One easy way of avoiding the most vulnerable areas is to give the most of frame a going over from the sides, keeping away from the hubs and BB shell and finishing the job by doing the hubs and BB areas from the front and rear. The Niner has full-length internal cable housings so I wasn't too worried about getting water in them, which is another potential problem. In most cases it's also best to steer clear of your handlebar tape too if you're planning to ride too soon after the wash because most modern types are nice and spongy and take a while to dry out.
I didn't have anything with me to wipe the bike down today, but fortunately they're pretty robust beasts. I bounced the Niner a couple of times to shake off the excess water. Before I ride tomorrow I'll wipe down the chain and relube it and the pivot points on my dérailleurs and we're good to go again.