Depends on what you mean by obsolete...Apple is done with the PPC architecture and the G5 chip. That being said, it is still a fine chip and you'll get good performance from native apps and Universal apps.
MS Office is still for PowerPC. You can find Photoshop for PPC for probably a good price.
What will you be using the machine for? You will be missing out on the dual core of an Intel chip, which helps in video encoding for ripping or creating DVDs, ripping CDs, video editing, etc.