reading the Cubase4 forum seems that...hmmm...patience is a good friend :)
looks like Steinberg dudes need to fix a bit of things (thinking that only 3 days after the official publication, they released a patch...).
Originally the C4 release was scheduled for later October: they anticipated in order to not lose clients/upgrades (Ableton and Cakewalk released their new versions just some days before...), but this was not a wise choice: it is not as much stable at is should be.

Of course, they will fix all: I will posticipate the upgrade 'til a TRUE solid-rock stable update :)

Most people like the new features in Cubase 4. I plan on upgrading to it shortly.

One word of warning (which is causing some venting in the cubase.net forums) is that Cubase4 for all it's improvements, does not support DX (unlike SX3). If you rely on DX plugins, you will need to test it with a vst>dx wrapper. Some who rely on DX Antares autotune (which apparently does not work in most wrappers) have cancelled their orders.

Steinberg did not mention this little fact in advance and are now taking some flak for it - they apologized for not informing but have stated conclusively that they are not supporting it and won't be making a wrapper of their own.

Cresta is correct in that one patch has already been released but it is typical practice for software to be almost 'beta version' these days on release and is not specific to Cubase - Sonar had bugfixes to 6 really fast after launch too.

The smart thing to do is bide your time and allow at least 2-3 months after the release date to get an upgrade or buy, by then there will probably have been 2-3 bugfixes/revisions and the most obvious and critical bugs will have been patched. This applies to any software, not just Cubase.

Take a look at the cubase forum for more opinion re: Cubase 4

On a positive note, people are liking the new VST instruments, control room, media bay and the updated fx plug-ins quite a bit...