I also run WP2.1 since this week, but it keep crashing about four times a day. Or it just consumes 99% of CPU and leaves me to kill the process. I haven’t found a cause yet.
Hope there will be new update and it will get better, because this is quit annoying.
There is a solution: Completely delete your old WP client and then install the 2.1 client. The runtime errors are due to overwriting the old dll files. A completely new install will fix this.