Few days ago I noticed that my hibernation process takes about 20 minutes. Everything else, restart, shutdown, standby were fast and worked fine. For me hibernation is very important for the portability. So I've google for answer. Finaly I found that disabling write-caching make hibernate to last about 15-20minutes, while it took about 20 second standard. I totally does not understand why it takes so long, I have 2GB of RAM, and all in all - in both situations all cache should be written to the disk.
Please consider if you want to enalbe write-caching, because it can cause a data loss in some situations.