The N900 is really disappointing in that it's a phone, and thus the price automatically gains a £100 - £200 "Don't worry, we can subsidize that" cost to make sure you buy it on contract instead of SIM-free. The Nokia N8x0s came out for quite reasonable prices compared to heavily subsidized phone.
I wanted to break out of this nasty phone contract habit and simply use a PAYG phone (very unlikely I'll top up with more than £10 every few months) alongside a data-only SIM on a rolling contract (Three currently do £15/pm with a dongle for £10 up front on a rolling, no ties contract) to use in my MiFi mobile router.
Losing the convenience of the iPhone's internet/GPS tie in and having readily accessible data is worth freeing up the money to buy any device that takes my fancy every 6-8 months.
Of course, the problem was that one of every 10 people buying a Nokia N8x0 had the inkling it was a phone and complained when they found out it wasn't. I think Nokia have stepped up to the plate this time and just thought "sod it" and made the N900 a phone. Not so good for those of us who want a practical, long-lived phone and a separate compliment of mobile computers.
I just bought an N810 recently from Play, should get it next week, software for NITs has matured so much since I last had an N810 so I'm sure it'll feed my geeky habits much better than an N900 might. If you like the look of the N900, grab an N810 fast whilst they're still available. For £130 it's a steal, and a much better buy than the SmartQ if only because of the awesome Maemo community.