All,
Today I installed the new Synology DSM 3.0-1337; Build Date: 2010/09/21 on my Synology NAS (DS 409slim).
DSM 3.0 Release NotesI was coming from version DSM 2.3-1157
The most important thing: after the upgrade all my data was still there

Did also some tests regarding performance, because I read some mixed responses regarding that.
For me it brought a huge performance boost on samba filesharing, see the 2 pictures of the test I did with Bench32 before and after the upgrade.
Did some testing with some bitrated Bluray movies that now and then had some stutter with previous DSM 2.3 -> gone!!
Any others here with a Synology NAS that are having the same good experience with this new version?
regards,
Maasbommel
PS. This test is done with lan cable connection .