Paul Hsieh from GeekPress just emailed me to ask about how happy I am with my purchase five months ago of an elliptical machine. I used to be an ardent runner, doing 12-15 miles per week, but my knees started hurting and after hearing horror stories from other runners I decided I needed to switch to a lower-impact exercise routine. So I bought the cheapest elliptical machine from my nearest Wal-Mart (under $150) and stuck it in my garage in front of the TV.
For the past five months I've used it 3-4 times per week for 30 minutes at a stretch, and it's been great. I put it together myself and the only shortcoming I noticed was that it required a generous drenching with WD-40 before it would run smoothly. The factory greasing wasn't sufficient to keep the machine from squeeking and rattling, but the WD-40 did the trick.
In use, I don't think the digital display is very accurate. It says that exercising for 30 minutes at one of the highest tension settings only results in me burning 12-15 calories, which I think it's low by a factor of 20 or so. A good rule of thumb is that running a mile burns around 100 calories, and the elliptical machine is quite a bit harder than running and utilizes far more muscle groups. The digital odometer and speedometer may be the roots of the problem, since after 30 minutes they show me having gone a mere 0.6 miles. Anyway, your mileage may vary... literally.
Having used my el cheapo model for five months, I don't see any reason buy a more expensive model. Mine doesn't have electronically variable tension or allow you to program "tracks" like some others do, but you can adjust the tension manually any time you want -- why pay hundreds of dollars more for a machine that does it for you? Mine seems to be holding up well under regular use, and I have no reason to believe that it won't last a few years.