Is it a usual thing for the Subaru "Boxer" engine to burn oil?

You don't say how many miles are on the car or how many miles you drive in a week but that is a lot. Try using 5w-30 or 10w-40 oil. Oil use can be from high miles or oil leaks from the head gaskets. Be glad you don't own a new Subaru that uses 0-20 oil! You could also try adding Lucas oil additive and see if that helps.

Synthetic oil costs a lot more than regular oil but is not used any faster or slower either. You can save money by going to regular oil. You don't say how often the oil is changed but going to every 3,000 miles might help some.

I've recently switched to Rotella T6 5w-40 and add it to my amazon subscription (16.63 after 15% off for 5 items) and get one every two months. That's 3 bucks cheaper than walmart. I am not as familiar with the oil burning as FoR but would like to hear more from JRH on your mileage / has the car sat long / long intervals of oil changes (stuck rings?). While your forester is running, take the oil cap off and slap your hand on the filler hole to seal it and feel the pulses as described in one post here: http://www.subaruforester.org/vbulletin/f88/how-much-blow-too- much-111031/ One poster also mentions Mobil 1 being the issue that they got away from. Which brand are you running? Keep researching!! :)

Some oils are much more volatile than others. Oils with low volatility will reduce oil consumption. I don't use or sell Amsoil but this report is informative. http://www.amsoil.com/lit/g3115.pdf

This is simpler than alluded to above: Subarus, having boxer motors that sit in oil at rest...and more importantly have horizontal strokes, consume oil, especially upon warmup...than "vertical" motors. The industry-wide move to 5w/20 oil did Subaru no favors...and then they shot themselves in the foot with 0w20 synth!! You will undoubtedly reduce oil consumption significantly by using 10w dino oils...or even good old 20w50 in hot climates. My favorite is he old euro-spec 15w40, but it's harder to find. Just stay away from skinny synths. Subarus' longevity isn't particularly predicated upon clean nor fussy-spec oil. It's more impoirtant to just keep the level reasonably full to reduce the chance of overheating, and thus increasing risk of head gasket failures or picking up rod bearing noises. If you know you're running 0w or 5w (or any synth) you can add a thickener (or just 20w/50) until the next oil change. Interestingly oil consumption may actually also diminish with use as the engine self-polishes over time. I've seen 175k mi 2.5i that neither consume nor even dirty up oil after 3k miles. Just keep the cooling system full along the way, and cover that oil stick's dot wet with thick stuff...and if it's cold out warm up for a miinute and don't rev above 3k until isothermal.