I recently bought a new Gateway 5408GT with Vista Premium pre-installed.
Core 2 Duo 4300 @ 1.8 GHz w/1GB DDR2. Integrated graphics card and Hi-def 7.1 sound. I bumped up the DDR2 to 4GB. The power supply was, if I remember, 300w. I added an nVidia 7950GT PCIe card. The PCIe card, however, requires more power than the stock configuration. So off to the store, again, to purchase a 500w Antec supply. Interestingly I was unable to utilize the 'upgrade now' software (cd) that came with the system. Correction, the software ran, but when I attempted to upgrade to Vista Ultimate, even though no 'installation buster' issues were detected, it failed. Fortunately the system did reset itself to the original configuration of Vista Premium with no ill effects. Phewww!
When I attempted to upgrade the previous pc I had (HP a450n, 3GHz, 800MHz fsb, 1.5 GB DDR) from WinXP Pro to Vista Premium, it did upgrade. However, much system hanging, and a few too many BSODs convinced me to re-install Win XP pro. So, I decided, time to buy a new PC.
And yes, I have had a couple (read literally 2) BSOD on Vista. But the system identified the error as related to software (Webroot SpySweeper) and provided a link to the manufacturer to update. I followed the link and, lo, it really was a functional link to Webroot with the download link for an updated version that is Vista compatible. A real improvement over the XP direction which 9 out of 10 time (in my limited experience) led to a 'don't know what software or driver caused the error, sorry' screen.
So, yes, I would wait a little while to upgrade. And unless you feel compelled to upgrade your present you present box, I would just build my own or buy one from an OEM in about 6 months as mentioned previously.
On a 1 to 10 scale with 1 being 'infernal machine in smoldering heap on front lawn' and 10 being 'PERFECTION in a box', I would give Vista (at least as I am experiencing it) a 6.
That's my 2 cents!