replace my iMac with a macbook air & external display?

When the latest macbook airs came out in mid 2011, I bought one on an impulse. I already have a late 2009 iMac (the base 21 inch model).

I feel like having these two computers is redundant, so I've been contemplating handing my iMac over to my parents and using the air and an external monitor for when I need ergonomics.

The macbook air is the base 13 inch configuration (mid 2011)
the iMac is the base 21 inch configuration (late 2009) with 12 GB of aftermarket ram added for no particular reason.

Here are my concerns:

-finding a display comparable to the iMac's: The thunderbolt display that Apple sells is really nice, but it's super expensive and too large for my taste.

-leaving the macbook air plugged in and on for long periods: Without a user replaceable battery, is this a wise option? I like having my iMac on all the time to stream content to my apple tv and airplay speakers.

-storage and expandability: The iMac has tons of usb ports as well as an ethernet jack, how can I replace these (again without resorting to the thunderbolt display?) How can I replace the 500 GB that my iMac provides? I do use it quite a bit.

Thanks

Do what I did. I have a MBP I wanted to initially use to stream (airplay) my iTunes library. I didnt want to leave it on all the time, however.

I got the MacMini instead. (see my sig as to which one I got) and since then, I have been able to watch my whole library via Apple TV or Apple Remote (iPad app) and so on. The mini is hooked up to my main TV and is working great as a Media server. Less money than a Thunderbolt display.

I am thinking about doing the same thing. I purchased a new Air yesterday and I am still in shock at how fast this darn thing is. I planned on getting an external monitor, but I am not even sure I need one now. Very happy with it so far!

I do as you described but with my

MB Pro 15". My Air has neither enough memory (only 4 GB) nor a large enough SSD (only 256 GB) for my daily purposes so I use my MB Pro (2.66GHz i7 processor, 8 GB RAM, 500 GB HDD). Have three USB slots on the rear of my 27" apple monitor, two in the MB Pro, and a Belkin USB hub with six more. Use them all.

OK. I will bite. You really have 11 USB devices plugged in?

Yes

2 printers
1 scansnap scanner
1 bassjump speaker
1 lexar card reader
1 external monitor
3 external HDDs
1 iOS connector cable
1 vacant

Yowser! You must have a huge desk

I just bought a 13" Air this week myself. I have to say it is amazing, fast, great keyboard. The only thing I don't like is the size of the SSD so I upgraded to 240GB Mercury Aura Pro Express SSD that will arrive wednesday. I am a little ****** at the pricing of the SSD's for the Air's I mean $411 for a 240GB SSD is a bit extreme but I need the extra space and I wasn't going to spend $300 more for the slow 256GB ssd.

Go with an Air and play with it, I have it attached to my 28" and it looks amazing, but its not even needed. I connected via HDMI (rocketfish mini to hdmi $24.99 @ worstbuy).