JR Pass - reserving tickets

Hi,
I will be buying a 7 day JR pass, and if possible would like to reserve my Shinkansen tickets before I get to Japan.
Is it possible to do this, as I cant exchange the actual pass to I get to Japan?

Also are there still disruptions to trains etc due to saving power following the earthquake.

Many thanks

The shinkansen lines operated by JR East can be reserved online here:
http://jreast-shinkansen-reservation.eki-net.com/pc/english/common/men...

The other shinkansen lines cannot be reserved until you have your actual pass exchanged in Japan. Please read the following pages for more details:
http://www.japan-guide.com/e/e2361.html
http://www.japan-guide.com/e/e2018.html

Also are there still disruptions to trains etc due to saving power following the earthquake.

Yes, some coastal train lines in Iwate, Miyagi and Fukushima are still disrupted, but this won't affect you unless you plan on visiting the coastal areas affected by the tsunami. It is also explained here:
http://www.japan-guide.com/news/0018.html

Also are there still disruptions to trains etc due to saving power following the earthquake.

I read over the "due to saving power".

Yes, the power saving measures still have a minor impact on some train lines until September 22. But they cannot be called "disruptions". It's only a minor thinning out of train frequency on some lines on weekdays between noon and 3pm. Most tourists will not notice it.

The Narita Express will return to its regular timetable tomorrow (September 3).