Just to let you know though don't be deleting your instacast app yet. Some aspects of the app look good some look bad and their is other different problems with it.
When you first open the app you will be greeted by a display of your Podcasts logo's. You get access via a button at the top of the screen to the Podcast section of the iTunes store and you can access your Podcasts by tapping on the logo. This page is where the problems start, I have previously have had to wait for more than 10 seconds for the app to be ready for me to use it. It's not like I am using this app on an old iPhone 2, I am using an iPhone 4 (yes I know it's not a 4s) which isn't normally a slow phone but this app makes it feel like it's powered by a steam engine. Please Apple I beg you look into your code and find out a way to speed it up, it's wrecking the user experience. Anyway rant over the home page also gives you access to the stations listing's.
This isn't amazingly designed but it does work sort of, you scroll from left to right at the top of the screen to change through the different categories and then up and down to change through the different "stations" in that section.
Anyway back to listening to Podcasts them self, once you have selected a Podcast to listen to you will be presented with a list of the available episodes, if you want to subscribe to a feed you tap on the title of the Podcast and it will present you with a selection of options from subscribe to auto-download new episodes and which order you want to display the episodes in (i.e. oldest first or newest first) but be careful because I found that if I selected for it to auto-download latest episodes it wont download just the newest one it will try and download every single episode produced because it hasn't seen the episode before so as far as the app is aware they are all new episodes(That is right get ready to pull your hair out). You can't delete episodes you have listened to/don't want from the app screen. You have to go into the iPod section of your iPhone and then select the Podcast section and then find the episode and then you can delete(What a faff).
When it comes the playing screen it's not really too much different to what you get from the standard iPod section on the iPhone the only real difference is the addition of two slightly useful buttons skip forward 30 seconds and skip back 10 seconds. An annoying thing is when you get to the end of the latest episode it don't just stop it will auto-download the previous episode and start playing it weather you are connected to WiFi or just your normal 3G, but where it gets good is if you tap the center of the screen it will slide up to unveil the tape deck,
Now this is a nice touch from the detail that the Apple design team have put into it from things like the side of the tape deck that has the most tape on it rotates slower than the side with less virtual tape on it like it would in real life. It also gives you access to more controls including a sleep timer to a share button which allows you to auto tweet what you are listening to and I am guessing that when iOS 6 comes out it will add Facebook to the options in the share section, then there is a "switch" which allows you to speed up and slow down the playback speed. The annoying thing is the high speed scrubbing bar which is very hard to use but this is just a little fly in the ointment of this section of the app which looks very nice and in my opinion very easy/pleasing to the eye.
So to sum up on the Apple Podcast App:
Should you get it? Well yes and no. If you already own instacast and it has all the Podcasts that you like to listen to then don't bother getting it. If you don't and you like listening to Podcasts but hate having to keep checking up to see if there is new episodes available then yeah sure just be willing to have to mess around a little at first till it realises that you have heard certain episodes before in the past, and are willing to put up with it playing random episodes that you might have listened to in the past even if it isn't downloaded.
My suggestion is that you do what I do and that is use the Podcast app to keep all your Podcasts up to date but use the iPod section on my iPhone to play all the episodes that you want to listen to when you want to listen to them and this I find is a happy medium that seams to work for me.
This app has potential to be a great app but it is being let down by lots of little things (i.e. Slowing the phone down and just being slow in general) but I believe that knowing what Apple have been like in the past these problems wont be around for long.