I hate to be "that guy" but this has been discussed at length several times recently, a search will be your friend.
I purchased my '99 E46 328i with 100k miles on it and put 78k miles on it in 4 years before I sold it. Mine had the premium package,and I swapped a set of M3 buckets into it for their better support and comfort. Very reliable, though not as much as the Miata I had for 4 years (basic maintenance only).
Electrical problems were minimal - the rain sensor died (good used replacement on eBay for <$20) and I had ongoing issues with a rear turn signal socket that I finally fixed by bending the inner contact to make more firm contact. BMW found out how cheap they could go on the electrics in the E46 and moved back to better stuff in the E46.
Mechanical reliability on the motor was pretty good - the inline 6 motor is nearly bulletproof and a real gem. The 5-speed tranny developed a common issue with a sticky bushing in a bore causing the shifter to not self-center when cold. Requires pulling the trans to replace a $2-ish part through the side of the case. I was waiting for the clutch to need to be replaced but when sold at 178k the original clutch still had a ton of life left. The valve cover gasket got brittle and leaked around 150k miles, easy replacement. The "oil separator" went bad on mine, another fairly common issue. Caused a surge in the idle when cold and a "hoot" sound but I didn't care enough to pull the intake to replace it and the associated vacuum lines. I replaced a water pump as preventative maintenance and the parts house pump blew up in short order, leading to one time non-destructive overheating (I was lucky). I still had the stock pump i had pulled out sitting on the shelf, threw it back in and all was fine. The radiators have a reputation for cracking the plastic inlet/outlet but mine was fine. Another common issue I experienced was the coolant expansion tank splitting. That and the water pump were the only 2 times I was ever stranded. Belts and tensioners are also easy DIY items.
Common suspension issues are control arms that need to be replaced about every 50-75k miles due to integral, non-replaceable ball joints wearing out. The control arm bushings are usually pretty worn by then also. Rear shock mounts should be changed for Z3 or M3 units with reinforcing plates, cheap and easy. Some cars had issues with rear subframe mount points tearing out of the body, just something to check for in a PPI. Mine was fine, and by no means babied. I did manage to tear a rear trailing arm bushing with a parking lot burnout (my fault), one of the few things I had to pay someone to do. I had a brake caliper seize but a rebuilt BMW caliper was on the shelf at the local AdvanAutoBoys type chain for under $50. Not something I've really heard of as an issue on these cars.
Maintenance costs aren't bad. They're easy to work on with a good set of Torx sockets (internal and external). Oil changes are simple, and the BMW oil is around $4.50/quart at the dealer, same as or cheaper than Mobil1 or other synthetics. Forget the "lifetime" fill as marked on the trans and diff, I think "lifetime" means "life of warranty". Go by the old-school maintenance schedules for those liquids.
If you're looking at 60-70k mile items, plan on control arms and bushings, probably brakes and rotors, and full fluid changes (oil/trans/dif/brake/coolant) and belts if they're cracked. Plugs are due at 100k miles, you may want to change them sooner but not necessarily required. Other than that, feed it premium gas, keep it clean (stock brake pads dust like crazy) and drive it like you stole it. Join BMWCCA for parts discounts at the local dealer, and mail order parts from online discounters as you're able to do, and the running costs are quite reasonable, especially considering the Ultimate Driving Experience you get out of it. I'd HIGHLY recommend going for it.
Read the FAQs and DIYs at E46fanatics.com for good info, though you'll have to wade through some fanboi & tooner crap, but nothing like you've dealt with on Honda boards.
Scott
). This has translated into very low operating costs and pretty amazing reliability. I'm assuming from things I've heard that I should expect more issues, including some electrical gremlins, with a BMW. Now that it's time to actually pull the trigger I'm feeling pretty anxious about what I might be getting myself into. 
