I think that might be related to bandwidth rather than processor utilization. There are a couple things you can do. One is to enable QoS (Quality of Service) in your router if it has that feature.

Another way is to put a limit on torrent bandwidth in Miro. Go to File -> Options -> Downloads and enable these two settings:

[x] Limit upstream bandwidth to: [ 38 ] KB/s
[x] Limit downstream bandwidth to: [ 115 ] KB/s

The numbers are only suggestions and depend on the speed of your Internet connection as well as how quickly you want your torrent downloads to complete. The lower the numbers, the more bandwidth will be available for other programs like Firefox, but also the slower your torrents will download. I calculated these starting values based on a 384 Kb/s upstream and 1.5 Mb/s downstream DSL, reserving 20% upstream and 40% downstream for other programs:

upstream limit = (upstream bandwidth in Kb/s / 8 b/B) * 80%
= (384 / 8) * 0.8
= 38 KB/s
downstream limit = (downstream bandwidth in Kb/s / 8 b/B) * 60%
= (1536 / 8) * 0.6
= 115 KB/s

This is such a good idea, I hope it is successful! The graphics on the adoption page are very nice. I think monthly sponsorship is a smart and easy way for users to continue ongoing funding for the project.

Our donation also helps promote open and independent media, a cause that I strongly believe deserves our support.

Actually I upgraded Miro from 1.2.8 to a beta of 2.0 with no problems. I had made a backup of my database at the time, but never needed it. During the beta I experienced various crashes, and most of those bugs affecting my setup have been fixed prior to the 2.0 release. Here are my relevant specs:
Miro 2.0 r9177
Windows Vista 32-bit SP1
3GB RAM
about 90GB free space on drive
2x2.0GHz Core2 Duo
nVidia 7900 GS with 256MB

I really don't understand some of the negative comments in this blog. I've been using versions of Miro 2 while it was still in beta, and it seems quite stable to me. I have Miro running almost 24/7, checking and downloading podcasts, often downloading some torrents, and acting as my primary media player. All that, and I haven't had a single crash since the release of Miro 2.0. Sure, there are bugs but the developers are actively working to fix them.

Like any open source project, the community is strongly encouraged to help out (see the "Open Source" link at the top of this page).

The new website is awesome! Very nicely done. I'm very impressed with the new Miro Guide as well. And of course, Miro 2.0 is a treat to use. Congratulations on an excellent release!

This build feels solid. I'm excited about the launch. Are there plans for marketing, similar to Spread Firefox?

It looks really nice! I like the infinite scrolling (though I must admit, at first I thought the paging tabs were buggy).