nhibernate, load-balancing, failover, and caching

Question

We have a server that uses NHibernate, and we would like to load balance multiple instances of this server. Our database is big, ~100 GB.

If we use a distributed second level cache like memcached or sharedcache, are there still potential data integrity issues?

And, why doesn't the first level cache need to be distributed?

Also, how can we mitigate the performance penalty of having to fetch a cache object on the wire, rather than from RAM?

And finally, if there are any other issues we need to be mindful of for this configuration, please let me know.

Many Thanks!