I use Heroku while building out or testing applications - the first dyno is free and additional are $36/month. You can handle a decent amount of traffic on 2-3 dynos. To keep dyno time down, set up workers to run only when needed.
It would be a good idea to plan ahead for your db needs - AWS is a good solution. Try to run you RDS in the same zone as Heroku.
I don't use textmate either but it seems like the graphical editor of choice among Mac users. I like Vi/m from the terminal and I've progressed to using IDE's as well.
Switching from Ubuntu 11.04 on your HP to Mac/OSX will add the following:
- ability to use applications only available to Mac/Windows (like Netflix, Office)
- can buy/use Textmate
- a smoother GUI to work/play in
- the religious euphoria that comes with using iStuff
Ubuntu is working hard to improve the UI and have things "just work" but it's still lacking general adoption as a third pc/user platform. My laptop is on 11.04 but desktop is still Windows7 (+ 11.04 in Virtualbox) for that reason.