I've had a few smartphones, not alot but the N1 is my 3-4th one. It's the best phone if ever owned. Not perfect but a valueable addition in my daily life.
One of the main reasons this phone is so good is Android. After my last phone I promised myself I would not by a Wndows Mobile phone again. The aggrevation was daily and not something I wanted in my life anymore. Android just works, free to use for all features with the choice (yes, not forced) yours to support the apps you want and affect your life positively.
Multitasking is key. Open up as much as you want and Android will take care of handling the memory successfully.
The N1 has the hardware features to handle what you and Android throughs at it. The N1 is not the only choice but it's a good one. Personally, I would prefer a physical keyboard but I am living okay with the compromise. And that may be the key, buy the right hardware and Android should give you a happy experience.