Thanks to this great site and all its contributing members, I was able to change out the spark plugs and coils on my 2006 325xi. I just wanted to share a couple pictures and notes regarding this process.
After having three coils fail within the span of a couple months, I decided that it was time to change the remaining three coils and do the spark plug change while I had the cowl and engine cover off.
I use the DIY guide as seen here:
http://www.e90post.com/forums/showthread.php?t=174217
Here's a picture of the used spark plugs. I only changed 5 of 6, because my dealership gave me a new plug when one of my coils went out.
As you can see it appears like all the plugs were original Bosch plugs. What was interesting was that the gap on all plugs had opened up to about .047" from the factory spec. which is .043"
Here's a close-up of one of the old plugs electrode.
The tools listed for use on the DIY guide are correct, but I ended up buying an extended spark plug socket from ECS tuning. Also, if you don't have some type of angular socket adapter, you'll need a stubby extension, around 3" to remove the spark plug for cylinder 5 because of the engine cross brace.
My initial impressions after I went on a test drive were good. I didn't have any CEL lights or uneven idle. I think double-checking the gaps with a spark plug tool and feeler gauges is the way to go. The start-up and idle were noticeably improved afterwards.
Also, as a final note I got all of my parts from partsgeek.com, I saved about $9 on each coil, and about $5 on each plug. The coils and plugs they sell are original Bosch and NGK, they're just not stamped with the BMW logo.