I was in the same situation, and the iPad has worked out great. My mother switched off her ancient dial-up modem to broadband at the same time, and is having a great time sending text messages, video chatting with the grandkids, watching instructional crocheting videos, playing logic puzzle games, chiming in on Facebook conversations when they're only minutes old instead of weeks old, etc. She feels far more independent with the iPad than she did on the PC because she's more willing to try something for herself (search for and download a game, for example) that she would have been afraid could screw up the PC before.
The only thing we've found that she can't do on the iPad so far is downloading maps to her new automotive GPS. She has fairly convenient access to desktop computers at the local library and doesn't mind stopping by there occasionally if there happens to be one purchase or video or website or whatever that she can't make work on the iPad.