I ran a 2006 Outback 2.5 for 10yrs and 100,000 miles with no mechanical issues.

Older Subarus seem to have traditonally burned through oil.

I noticed the engine was burning oil quite early on - the older 2.5 engines I think suffered quite badly from oil usage, but as long as you checked the level regularly and kept it topped up, they were pretty much bombproof. Mine wasn't so bad, but I noticed they changed from from Shell Helix to a thicker Castrol GTX at about the 2nd or 3rd service - they explained the smaller molecules in the Helix oil were more prone to escape than the thicker Castrol. They used to always give you a litre of the Helix oil to take home at each service - presumably to encourage owners to check the oil level. Once they changed to Castrol they stopped this and, to be fair, oil consumption did drop off. They did charge for the 'free' oil, however!

My brother-in-law never checked his oil level (same car as mine) and his engine ate itself after about 80,000miles.

I think they've solved the oil consumption issues on the new 2.5 - keep your eye on it but do use the recommended viscosity. If there is ever an issue, Subaru will change the recommended oil in their maintenance alerts.

If it states 0W-20, then use 0W-20 !!!

I second that!

The differences between viscosity may be small but so too are the bearing clearances - measured in microns!