Lens correction is near the top of my wish list; I have to use a PTLens plugin on some images and then open the resultant Tiff file in Photoshop to make a more compact version (PTLens is saving 16-bit Tiff files). I'd love to be able to avoid that! (Yes, Photoshop can correct the images too).
My relationship with Aperture is also a love/hate relationship due to its performance and resource use problems.
I chose Aperture over Lightroom for a variety of reasons, including Faces, the user interface, and Photobook integration. I also hoped that transition my iPhoto library would be smoother than if using LR. The demo of LR3 was however noticeably more efficient, but I just didn't like the interface as much.
However, Aperture has turned out to be extremely resource intensive: Despite having a referenced library on an external FW800 drive, the Aperture library is massive, eating up 30 gigabytes of HD space so far just for thumbnails, and that's with Previews turned off. Lightroom, even though I didn't have so many photos imported when I was trialling it, didn't create a massive library. And its performance on my 2008 iMac with 4Gb was smooth, whereas performance of Aperture is variable, sometimes grinding to a stuttering halt. Having consumed a large proportion of my spare HD space, I'm having to shift more and more things to an external drive, and hence have another drive to back that up. So lack of HD space at various times is one issue with smooth performance, as with Photoshop it consumes a lot of temporary space. My 2008 iMac is maxed at 4Gb (not sure if it can unofficially take more), otherwise more RAM would be a consideration. But really, 4Gb should be plenty of RAM, and it shouldn't consume so much HD space with all its thumbnails! I'm a little disillusioned, and now that LR4 is out, the clock is ticking for them to come out with an update very soon to address some of these issues! I know I'm not the only one seeing this massive resource usage. I understand why they wouldn't want to clutter their iPad event with an Aperture announcement, they often want to keep the focus and have a separate announcement for something like this, and hopefully it will be soon! 30Gb just for thumbnails is ridiculous!