Hmm...I could see how it might if in your case the PSU was very close to the fan in the top, it might disrupt some of the airflow through the PSU, which in turn may result in the PSU running a little hot.
Other than that, I can't think how that would be detrimental, since hot air does rise, and would at least in theory would draw the heat out of the case faster.
700MHz Pentium III@933Mhz
256MB Mushkin PC133
nVidia GeForce2 GTS 32MB
WD Ultra2 10k rpm 9.1GB
Generic 52x CD-ROM
Tekram DC-390U2W SCSI
Yamaha CRW8424S CD-RW SCSI-2
Shuttle AK31v3.1 AMD XP1700+ 256MB Samsung PC2100 DDR nVidia GeForce2 GTS 32MB
Maxtor 40GB D740X 7200RPM ATA-133 Generic 52x CD-ROM Tekram DC-390U2W SCSI Yamaha CRW8424S CD-RW SCSI-2