My girlfriend was in roughly the same boat a month ago. Her 8+ year old P4 desktop hasn't been turned on in many months. She planned to replace it soon.
I bought myself a Nexus 7 to take with me for my computing needs (video games, video watching, IRC, eBook reading, remote access to my home network, etc.) while at her place. She saw how much I could get done with it and quickly changed her mind about buying a new desktop/laptop.
She picked up an ASUS Transformer TF300T at a recent sale from Best Buy and has since used it more than she ever would have used a full blown PC. She previously used her iPhone to get her basic tasks done (tons of email, casual games, web surfing, YouTube, Pandora) but since having the tablet she only uses her iPhone as a phone (and no longer suffers with that tiny screen).
Posted laying in bed from my Nexus 7 with her playing Zen Pinball on her Transformer.