I would wait for 4, its probably going to the same touch sensor technology in iphone 5 that'll make it slimmer. Originally 3 was going to use the same thinner technology but it was perfected so you had this bulky screen that eats up battery. Plus it'll probably use the new dock connector also, it be a hassle to carry 2 different types.
Disclaimer: as an apple share holder since 98 dollars, i will push you to buy more apple products. I dont own any ipads since 1 (which I sold). I like it but I dont find enough use for it. I do own 2 nexus 7 tablets (just came yesterday) 🙂 Im not a huge android fan but I just need to try these things out 🙂